Package 'tidybayes'

Description

tidybayes is an R package that aims to make it easy to integrate popular Bayesian modeling methods into a tidy data + ggplot workflow.

Details

Tidy data frames (one observation per row) are particularly convenient for use in a variety of R data manipulation and visualization packages (Wickham 2014). However, when using Bayesian modeling functions like JAGS or Stan in R, we often have to translate this data into a form the model understands, and then after running the model, translate the resulting sample (or predictions) into a more tidy format for use with other R functions. tidybayes aims to simplify these two common (often tedious) operations. It also provides a variety of ggplot geometries aimed at making the visualization of model output easier.

For a comprehensive overview of the package, see vignette("tidybayes"). For overviews aimed at the rstanarm and brms packages, see vignette("tidy-rstanarm") and vignette("tidy-brms"). For an overview of the majority of geoms in the ggdist/tidybayes family, see vignette("slabinterval", package = "ggdist").

For a list of supported models, see tidybayes-models.

Author(s)

Maintainer: Matthew Kay [email protected]

Other contributors:

• Timothy Mastny [email protected] [contributor]

References

Wickham, Hadley. (2014). Tidy data. Journal of Statistical Software, 59(10), 1-23. doi:10.18637/jss.v059.i10.

See Also

Useful links:

• https://mjskay.github.io/tidybayes/

• https://github.com/mjskay/tidybayes/

• Report bugs at https://github.com/mjskay/tidybayes/issues

Description

Add draws from a matrix of draws (usually draws from a predictive distribution) to a data frame in tidy format. This is a generic version of add_predicted_draws() that can be used with model types that have their own prediction functions that are not yet supported by tidybayes.

Usage

add_draws(data, draws, value = ".value")

Arguments

Details

Given a data frame with M rows and an N by M matrix of N draws, adds a .row, .draw, and .value column (or another name if value is set) to data, and expands data into a long-format dataframe of draws.

add_epred_draws(df, m) is roughly equivalent to add_draws(df, posterior_epred(m, newdata = df)), except that add_epred_draws standardizes argument names and values across packages and has additional features for some model types (like handling ordinal responses and distributional parameters in brms).

add_predicted_draws(df, m) is roughly equivalent to add_draws(df, posterior_predict(m, newdata = df)), except that add_predicted_draws standardizes argument names and values across packages.

Value

A data frame (actually, a tibble) with a .row column (a factor grouping rows from the input data), a .draw column (a unique index corresponding to each draw from the distribution), and a column with its name specified by the value argument (default is .value) containing the values of draws from draws. The data frame is grouped by all rows in data plus the .row column.

Author(s)

Matthew Kay

See Also

add_predicted_draws(), add_draws()

Examples

## Not run: 

library(ggplot2)
library(dplyr)
library(brms)
library(modelr)

theme_set(theme_light())

m_mpg = brm(mpg ~ hp * cyl, data = mtcars,
  # 1 chain / few iterations just so example runs quickly
  # do not use in practice
  chains = 1, iter = 500)

# plot posterior predictive intervals
mtcars %>%
  group_by(cyl) %>%
  data_grid(hp = seq_range(hp, n = 101)) %>%
  # the line below is roughly equivalent to add_epred_draws(m_mpg), except
  # that it does not standardize arguments across model types.
  add_draws(posterior_epred(m_mpg, newdata = .)) %>%
  ggplot(aes(x = hp, y = mpg, color = ordered(cyl))) +
  stat_lineribbon(aes(y = .value), alpha = 0.25) +
  geom_point(data = mtcars) +
  scale_fill_brewer(palette = "Greys")


## End(Not run)

Description

Given a data frame and a model, adds draws from the linear/link-level predictor, the expectation of the posterior predictive, the posterior predictive, or the residuals of a model to the data frame in a long format.

Usage

add_epred_draws(
  newdata,
  object,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL
)

epred_draws(
  object,
  newdata,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL
)

## Default S3 method:
epred_draws(
  object,
  newdata,
  ...,
  value = ".epred",
  seed = NULL,
  category = NULL
)

## S3 method for class 'stanreg'
epred_draws(
  object,
  newdata,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL
)

## S3 method for class 'brmsfit'
epred_draws(
  object,
  newdata,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL
)

add_linpred_draws(
  newdata,
  object,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL,
  n
)

linpred_draws(
  object,
  newdata,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL,
  n,
  scale
)

## Default S3 method:
linpred_draws(
  object,
  newdata,
  ...,
  value = ".linpred",
  seed = NULL,
  category = NULL
)

## S3 method for class 'stanreg'
linpred_draws(
  object,
  newdata,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL
)

## S3 method for class 'brmsfit'
linpred_draws(
  object,
  newdata,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  dpar = NULL
)

add_predicted_draws(
  newdata,
  object,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  n
)

predicted_draws(
  object,
  newdata,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  n,
  prediction
)

## Default S3 method:
predicted_draws(
  object,
  newdata,
  ...,
  value = ".prediction",
  seed = NULL,
  category = ".category"
)

## S3 method for class 'stanreg'
predicted_draws(
  object,
  newdata,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category"
)

## S3 method for class 'brmsfit'
predicted_draws(
  object,
  newdata,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category"
)

add_residual_draws(
  newdata,
  object,
  ...,
  value = ".residual",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  n
)

residual_draws(
  object,
  newdata,
  ...,
  value = ".residual",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category",
  n,
  residual
)

## Default S3 method:
residual_draws(object, newdata, ...)

## S3 method for class 'brmsfit'
residual_draws(
  object,
  newdata,
  ...,
  value = ".residual",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  category = ".category"
)

Arguments

Details

Consider a model like:

$\begin{array}{rcl} y &\sim& \textrm{SomeDist}(\theta_1, \theta_2)\\ f_1(\theta_1) &=& \alpha_1 + \beta_1 x\\ f_2(\theta_2) &=& \alpha_2 + \beta_2 x \end{array}$

This model has:

• an outcome variable, $y$

• a response distribution, $\textrm{SomeDist}$, having parameters $\theta_1$ (with link function $f_1$) and $\theta_2$ (with link function $f_2$)

• a single predictor, $x$

• coefficients $\alpha_1$, $\beta_1$, $\alpha_2$, and $\beta_2$

We fit this model to some observed data, $y_\textrm{obs}$, and predictors, $x_\textrm{obs}$. Given new values of predictors, $x_\textrm{new}$, supplied in the data frame newdata, the functions for posterior draws are defined as follows:

• add_predicted_draws() adds draws from the posterior predictive distribution, $p(y_\textrm{new} | x_\textrm{new}, y_\textrm{obs})$, to the data. It corresponds to rstanarm::posterior_predict() or brms::posterior_predict().

• add_epred_draws() adds draws from the expectation of the posterior predictive distribution, aka the conditional expectation, $E(y_\textrm{new} | x_\textrm{new}, y_\textrm{obs})$, to the data. It corresponds to rstanarm::posterior_epred() or brms::posterior_epred(). Not all models support this function.

• add_linpred_draws() adds draws from the posterior linear predictors to the data. It corresponds to rstanarm::posterior_linpred() or brms::posterior_linpred(). Depending on the model type and additional parameters passed, this may be:

  • The untransformed linear predictor, e.g. $p(f_1(\theta_1) | x_\textrm{new}, y_\textrm{obs})$ = $p(\alpha_1 + \beta_1 x_\textrm{new} | x_\textrm{new}, y_\textrm{obs})$. This is returned by add_linpred_draws(transform = FALSE) for brms and rstanarm models. It is analogous to type = "link" in predict.glm().

  • The inverse-link transformed linear predictor, e.g. $p(\theta_1 | x_\textrm{new}, y_\textrm{obs})$ = $p(f_1^{-1}(\alpha_1 + \beta_1 x_\textrm{new}) | x_\textrm{new}, y_\textrm{obs})$. This is returned by add_linpred_draws(transform = TRUE) for brms and rstanarm models. It is analogous to type = "response" in predict.glm().

  NOTE: add_linpred_draws(transform = TRUE) and add_epred_draws() may be equivalent but are not guaranteed to be. They are equivalent when the expectation of the response distribution is equal to its first parameter, i.e. when $E(y) = \theta_1$. Many distributions have this property (e.g. Normal distributions, Bernoulli distributions), but not all. If you want the expectation of the posterior predictive, it is best to use add_epred_draws() if available, and if not available, verify this property holds prior to using add_linpred_draws().

• add_residual_draws() adds draws from residuals, $p(y_\textrm{obs} - y_\textrm{new} | x_\textrm{new}, y_\textrm{obs})$, to the data. It corresponds to brms::residuals.brmsfit().

The corresponding functions without add_ as a prefix are alternate spellings with the opposite order of the first two arguments: e.g. add_predicted_draws(newdata, object) versus predicted_draws(object, newdata). This facilitates use in data processing pipelines that start either with a data frame or a model.

Given equal choice between the two, the spellings prefixed with add_ are preferred.

Value

A data frame (actually, a tibble) with a .row column (a factor grouping rows from the input newdata), .chain column (the chain each draw came from, or NA if the model does not provide chain information), .iteration column (the iteration the draw came from, or NA if the model does not provide iteration information), and a .draw column (a unique index corresponding to each draw from the distribution). In addition, epred_draws includes a column with its name specified by the epred argument (default ".epred"); linpred_draws includes a column with its name specified by the linpred argument (default ".linpred"), and predicted_draws contains a column with its name specified by the .prediction argument (default ".prediction"). For convenience, the resulting data frame comes grouped by the original input rows.

Author(s)

Matthew Kay

See Also

add_draws() for the variant of these functions for use with packages that do not have explicit support for these functions yet. See spread_draws() for manipulating posteriors directly.

Examples

## Not run: 

library(ggplot2)
library(dplyr)
library(brms)
library(modelr)

theme_set(theme_light())

m_mpg = brm(mpg ~ hp * cyl, data = mtcars,
  # 1 chain / few iterations just so example runs quickly
  # do not use in practice
  chains = 1, iter = 500)

# draw 100 lines from the posterior means and overplot them
mtcars %>%
  group_by(cyl) %>%
  data_grid(hp = seq_range(hp, n = 101)) %>%
  # NOTE: only use ndraws here when making spaghetti plots; for
  # plotting intervals it is always best to use all draws (omit ndraws)
  add_epred_draws(m_mpg, ndraws = 100) %>%
  ggplot(aes(x = hp, y = mpg, color = ordered(cyl))) +
  geom_line(aes(y = .epred, group = paste(cyl, .draw)), alpha = 0.25) +
  geom_point(data = mtcars)

# plot posterior predictive intervals
mtcars %>%
  group_by(cyl) %>%
  data_grid(hp = seq_range(hp, n = 101)) %>%
  add_predicted_draws(m_mpg) %>%
  ggplot(aes(x = hp, y = mpg, color = ordered(cyl))) +
  stat_lineribbon(aes(y = .prediction), .width = c(.99, .95, .8, .5), alpha = 0.25) +
  geom_point(data = mtcars) +
  scale_fill_brewer(palette = "Greys")


## End(Not run)

Description

Given a data frame and a model, adds rvars of draws from the linear/link-level predictor, the expectation of the posterior predictive, or the posterior predictive to the data frame.

Usage

add_epred_rvars(
  newdata,
  object,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

epred_rvars(
  object,
  newdata,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

## Default S3 method:
epred_rvars(
  object,
  newdata,
  ...,
  value = ".epred",
  seed = NULL,
  dpar = NULL,
  columns_to = NULL
)

## S3 method for class 'stanreg'
epred_rvars(
  object,
  newdata,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

## S3 method for class 'brmsfit'
epred_rvars(
  object,
  newdata,
  ...,
  value = ".epred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

add_linpred_rvars(
  newdata,
  object,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

linpred_rvars(
  object,
  newdata,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

## Default S3 method:
linpred_rvars(
  object,
  newdata,
  ...,
  value = ".linpred",
  seed = NULL,
  dpar = NULL,
  columns_to = NULL
)

## S3 method for class 'stanreg'
linpred_rvars(
  object,
  newdata,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

## S3 method for class 'brmsfit'
linpred_rvars(
  object,
  newdata,
  ...,
  value = ".linpred",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  dpar = NULL,
  columns_to = NULL
)

add_predicted_rvars(
  newdata,
  object,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  columns_to = NULL
)

predicted_rvars(
  object,
  newdata,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  columns_to = NULL
)

## Default S3 method:
predicted_rvars(
  object,
  newdata,
  ...,
  value = ".prediction",
  seed = NULL,
  columns_to = NULL
)

## S3 method for class 'stanreg'
predicted_rvars(
  object,
  newdata,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  columns_to = NULL
)

## S3 method for class 'brmsfit'
predicted_rvars(
  object,
  newdata,
  ...,
  value = ".prediction",
  ndraws = NULL,
  seed = NULL,
  re_formula = NULL,
  columns_to = NULL
)

Arguments

Details

Consider a model like:

$\begin{array}{rcl} y &\sim& \textrm{SomeDist}(\theta_1, \theta_2)\\ f_1(\theta_1) &=& \alpha_1 + \beta_1 x\\ f_2(\theta_2) &=& \alpha_2 + \beta_2 x \end{array}$

This model has:

• an outcome variable, $y$

• a response distribution, $\textrm{SomeDist}$, having parameters $\theta_1$ (with link function $f_1$) and $\theta_2$ (with link function $f_2$)

• a single predictor, $x$

• coefficients $\alpha_1$, $\beta_1$, $\alpha_2$, and $\beta_2$

We fit this model to some observed data, $y_\textrm{obs}$, and predictors, $x_\textrm{obs}$. Given new values of predictors, $x_\textrm{new}$, supplied in the data frame newdata, the functions for posterior draws are defined as follows:

• add_predicted_rvars() adds rvars containing draws from the posterior predictive distribution, $p(y_\textrm{new} | x_\textrm{new}, y_\textrm{obs})$, to the data. It corresponds to rstanarm::posterior_predict() or brms::posterior_predict().

• add_epred_rvars() adds rvars containing draws from the expectation of the posterior predictive distribution, aka the conditional expectation, $E(y_\textrm{new} | x_\textrm{new}, y_\textrm{obs})$, to the data. It corresponds to rstanarm::posterior_epred() or brms::posterior_epred(). Not all models support this function.

• add_linpred_rvars() adds rvars containing draws from the posterior linear predictors to the data. It corresponds to rstanarm::posterior_linpred() or brms::posterior_linpred(). Depending on the model type and additional parameters passed, this may be:

  • The untransformed linear predictor, e.g. $p(f_1(\theta_1) | x_\textrm{new}, y_\textrm{obs})$ = $p(\alpha_1 + \beta_1 x_\textrm{new} | x_\textrm{new}, y_\textrm{obs})$. This is returned by add_linpred_rvars(transform = FALSE) for brms and rstanarm models. It is analogous to type = "link" in predict.glm().

  • The inverse-link transformed linear predictor, e.g. $p(\theta_1 | x_\textrm{new}, y_\textrm{obs})$ = $p(f_1^{-1}(\alpha_1 + \beta_1 x_\textrm{new}) | x_\textrm{new}, y_\textrm{obs})$. This is returned by add_linpred_rvars(transform = TRUE) for brms and rstanarm models. It is analogous to type = "response" in predict.glm().

  NOTE: add_linpred_rvars(transform = TRUE) and add_epred_rvars() may be equivalent but are not guaranteed to be. They are equivalent when the expectation of the response distribution is equal to its first parameter, i.e. when $E(y) = \theta_1$. Many distributions have this property (e.g. Normal distributions, Bernoulli distributions), but not all. If you want the expectation of the posterior predictive, it is best to use add_epred_rvars() if available, and if not available, verify this property holds prior to using add_linpred_rvars().

The corresponding functions without add_ as a prefix are alternate spellings with the opposite order of the first two arguments: e.g. add_predicted_rvars(newdata, object) versus predicted_rvars(object, newdata). This facilitates use in data processing pipelines that start either with a data frame or a model.

Given equal choice between the two, the spellings prefixed with add_ are preferred.

Value

A data frame (actually, a tibble) equal to the input newdata with additional columns added containing rvars representing the requested predictions or fits.

Author(s)

Matthew Kay

See Also

add_predicted_draws() for the analogous functions that use a long-data-frame-of-draws format instead of a data-frame-of-rvars format. See spread_rvars() for manipulating posteriors directly.

Examples

## Not run: 

library(ggplot2)
library(dplyr)
library(posterior)
library(brms)
library(modelr)

theme_set(theme_light())

m_mpg = brm(mpg ~ hp * cyl, data = mtcars, family = lognormal(),
  # 1 chain / few iterations just so example runs quickly
  # do not use in practice
  chains = 1, iter = 500)

# Look at mean predictions for some cars (epred) and compare to
# the exponeniated mu parameter of the lognormal distribution (linpred).
# Notice how they are NOT the same. This is because exp(mu) for a
# lognormal distribution is equal to its median, not its mean.
mtcars %>%
  select(hp, cyl, mpg) %>%
  add_epred_rvars(m_mpg) %>%
  add_linpred_rvars(m_mpg, value = "mu") %>%
  mutate(expmu = exp(mu), .epred - expmu)

# plot intervals around conditional means (epred_rvars)
mtcars %>%
  group_by(cyl) %>%
  data_grid(hp = seq_range(hp, n = 101)) %>%
  add_epred_rvars(m_mpg) %>%
  ggplot(aes(x = hp, color = ordered(cyl), fill = ordered(cyl))) +
  stat_lineribbon(aes(dist = .epred), .width = c(.95, .8, .5), alpha = 1/3) +
  geom_point(aes(y = mpg), data = mtcars) +
  scale_color_brewer(palette = "Dark2") +
  scale_fill_brewer(palette = "Set2")

# plot posterior predictive intervals (predicted_rvars)
mtcars %>%
  group_by(cyl) %>%
  data_grid(hp = seq_range(hp, n = 101)) %>%
  add_predicted_rvars(m_mpg) %>%
  ggplot(aes(x = hp, color = ordered(cyl), fill = ordered(cyl))) +
  stat_lineribbon(aes(dist = .prediction), .width = c(.95, .8, .5), alpha = 1/3) +
  geom_point(aes(y = mpg), data = mtcars) +
  scale_color_brewer(palette = "Dark2") +
  scale_fill_brewer(palette = "Set2")


## End(Not run)

Description

Combines the chain and iteration columns of a tidy data frame of draws from a Bayesian model fit into a new column that can uniquely identify each draw. Generally speaking not needed for pure tidybayes code, as tidybayes functions now automatically include a .draw column, but can be useful when interacting with packages that do not provide such a column.

Usage

combine_chains(data, chain = .chain, iteration = .iteration, into = ".draw")

Arguments

Value

A data frame of tidy draws with a combined iteration column

Author(s)

Matthew Kay

See Also

emmeans::emmeans()

Examples

library(magrittr)
library(coda)

data(line, package = "coda")

# The `line` posterior has two chains with 200 iterations each:
line %>%
  tidy_draws() %>%
  summary()

# combine_chains combines the chain and iteration column into the .draw column.
line %>%
  tidy_draws() %>%
  combine_chains() %>%
  summary()

Description

Given posterior draws from a Bayesian model in long format (e.g. as returned by spread_draws()), compare the value of a variable in those draws across different paired combinations of levels of a factor.

Usage

compare_levels(
  data,
  variable,
  by,
  fun = `-`,
  comparison = "default",
  draw_indices = c(".chain", ".iteration", ".draw"),
  ignore_groups = ".row"
)

Arguments

Details

This function simplifies conducting comparisons across levels of some variable in a tidy data frame of draws. It applies fun to all values of variable for each pair of levels of by as selected by comparison. By default, all pairwise comparisons are generated if by is an unordered factor and ordered comparisons are made if by is ordered.

The included comparison types are:

• ordered: compare each level i with level i - 1; e.g. fun(i, i - 1)

• pairwise: compare each level of by with every other level.

• control: compare each level of by with the first level of by. If you wish to compare with a different level, you can first apply relevel() to by to set the control (reference) level.

• default: use ordered if is.ordered(by) and pairwise otherwise.

Value

A data.frame with the same columns as data, except that the by column contains a symbolic representation of the comparison of pairs of levels of by in data, and variable contains the result of that comparison.

Author(s)

Matthew Kay

See Also

emmeans_comparison() to use emmeans-style contrast methods with compare_levels().

Examples

library(dplyr)
library(ggplot2)

data(RankCorr, package = "ggdist")

# Let's do all pairwise comparisons of b[i,1]:
RankCorr %>%
  spread_draws(b[i,j]) %>%
  filter(j == 1) %>%
  compare_levels(b, by = i) %>%
  median_qi()

# Or let's plot all comparisons against the first level (control):
RankCorr %>%
  spread_draws(b[i,j]) %>%
  filter(j == 1) %>%
  compare_levels(b, by = i, comparison = control) %>%
  ggplot(aes(x = b, y = i)) +
  stat_halfeye()

# Or let's plot comparisons of all levels of j within
# all levels of i
RankCorr %>%
  spread_draws(b[i,j]) %>%
  group_by(i) %>%
  compare_levels(b, by = j) %>%
  ggplot(aes(x = b, y = j)) +
  stat_halfeye() +
  facet_grid(cols = vars(i))

Description

Compose data into a list suitable to be passed into a Bayesian model (JAGS, BUGS, Stan, etc).

Usage

compose_data(..., .n_name = n_prefix("n"))

Arguments

Details

This function recursively translates each argument into list elements using as_data_list(), merging all resulting lists together. By default this means that:

• numerics are included as-is.

• logicals are translated into numeric using as.numeric().

• factors are translated into numeric using as.numeric(), and an additional element named .n_name(argument_name) is added with the number of levels in the factor. The default .n_name function prefixes "n_" before the factor name; e.g. a factor named foo will have an element named n_foo added containing the number of levels in foo.

• character vectors are converted into factors then translated into numeric in the same manner as factors are.

• lists are translated by translating all elements of the list (recursively) and adding them to the result.

• data.frames are translated by translating every column of the data.frame and adding them to the result. A variable named "n" (or .n_name(argument_name) if the data.frame is passed as a named argument argument_name) is also added containing the number of rows in the data frame.

• NULL values are dropped. Setting a named argument to NULL can be used to drop that item from the resulting list (if an unwanted element was added to the list by a previous argument, such as a column from a data frame that is not needed in the model).

• all other types are dropped (and a warning given)

As in functions like dplyr::mutate(), each expression is evaluated in an environment containing the data list built up so far.

For example, this means that if the first argument to compose_data is a data frame, subsequent arguments can include direct references to columns from that data frame. This allows you, for example, to easily use x_at_y() to generate indices for nested models.

If you wish to add support for additional types not described above, provide an implementation of as_data_list() for the type. See the implementations of as_data_list.numeric, as_data_list.logical, etc for examples.

Value

A list where each element is a translated variable as described above.

Author(s)

Matthew Kay

See Also

x_at_y(), spread_draws(), gather_draws().

Examples

library(magrittr)

df = data.frame(
  plot = factor(paste0("p", rep(1:8, times = 2))),
  site = factor(paste0("s", rep(1:4, each = 2, times = 2)))
)

# without changing `.n_name`, compose_data() will prefix indices
# with "n" by default
df %>%
  compose_data()

# you can use n_prefix() to define a different prefix (e.g. "N"):
df %>%
  compose_data(.n_name = n_prefix("N"))

# If you have nesting, you may want a nested index, which can be generated using x_at_y()
# Here, site[p] will give the site for plot p
df %>%
  compose_data(site = x_at_y(site, plot))

Description

Functions used by compose_data() to create lists of data suitable for input into a Bayesian modeling function. These functions typically should not be called directly (instead use compose_data()), but are exposed for the rare cases in which you may need to provide your own conversion routines for a data type not already supported (see Details).

Usage

data_list(...)

as_data_list(object, name = "", ...)

## Default S3 method:
as_data_list(object, name = "", ...)

## S3 method for class 'numeric'
as_data_list(object, name = "", scalar_as_array = FALSE, ...)

## S3 method for class 'logical'
as_data_list(object, name = "", ...)

## S3 method for class 'factor'
as_data_list(object, name = "", .n_name = n_prefix("n"), ...)

## S3 method for class 'character'
as_data_list(object, name = "", ...)

## S3 method for class 'list'
as_data_list(object, name = "", ...)

## S3 method for class 'data.frame'
as_data_list(object, name = "", .n_name = n_prefix("n"), ...)

## S3 method for class 'data_list'
as_data_list(object, name = "", ...)

Arguments

Details

data_list creates a list with class c("data_list", "list") instead of c("list"), but largely otherwise acts like the list() function.

as_data_list recursively translates its first argument into list elements, concatenating all resulting lists together. By default this means that:

• numerics are included as-is.

• logicals are translated into numeric using as.numeric().

• factors are translated into numeric using as.numeric(), and an additional element named .n_name(name) is added with the number of levels in the factor.

• character vectors are converted into factors then translated into numeric in the same manner as factors are.

• lists are translated by translating all elements of the list (recursively) and adding them to the result.

• data.frames are translated by translating every column of the data.frame and adding them to the result. A variable named "n" (or .n_name(name) if name is not "") is also added containing the number of rows in the data frame.

• all other types are dropped (and a warning given)

If you wish to add support for additional types not described above, provide an implementation of as_data_list() for the type. See the implementations of as_data_list.numeric, as_data_list.logical, etc for examples.

Value

An object of class c("data_list", "list"), where each element is a translated variable as described above.

Author(s)

Matthew Kay

See Also

compose_data().

Examples

# Typically these functions should not be used directly.
# See the compose_data function for examples of how to translate
# data in lists for input to Bayesian modeling functions.

Description

Generates a data frame of bins representing the kernel density (or histogram) of a vector, suitable for use in generating predictive distributions for visualization. These functions were originally designed for use with the now-deprecated predict_curve(), and may be deprecated in the future.

Usage

density_bins(x, n = 101, ...)

histogram_bins(x, n = 30, breaks = n, ...)

Arguments

Details

These functions are simple wrappers to density() and hist() that compute density estimates and return their results in a consistent format: a data frame of bins suitable for use with the now-deprecated predict_curve().

density_bins computes a kernel density estimate using density().

histogram_bins computes a density histogram using hist().

Value

A data frame representing bins and their densities with the following columns:

Author(s)

Matthew Kay

See Also

See add_predicted_draws() and stat_lineribbon() for a better approach. These functions may be deprecated in the future.

Examples

## Not run: 

library(ggplot2)
library(dplyr)
library(brms)
library(modelr)

theme_set(theme_light())

m_mpg = brm(mpg ~ hp * cyl, data = mtcars)

step = 1
mtcars %>%
  group_by(cyl) %>%
  data_grid(hp = seq_range(hp, by = step)) %>%
  add_predicted_draws(m_mpg) %>%
  summarise(density_bins(.prediction), .groups = "drop") %>%
  ggplot() +
  geom_rect(aes(
    xmin = hp - step/2, ymin = lower, ymax = upper, xmax = hp + step/2,
    fill = ordered(cyl), alpha = density
  )) +
  geom_point(aes(x = hp, y = mpg, fill = ordered(cyl)), shape = 21, data = mtcars) +
  scale_alpha_continuous(range = c(0, 1)) +
  scale_fill_brewer(palette = "Set2")


## End(Not run)

Description

Convert emmeans contrast methods into comparison functions suitable for use with compare_levels().

Usage

emmeans_comparison(method, ...)

Arguments

Details

Given an emmeans contrast method name as a string (e.g., "pairwise", "trt.vs.ctrl", etc) or an emmeans-style contrast function (e.g., emmeans::pairwise.emmc, emmeans::trt.vs.ctrl.emmc, etc), emmeans_comparison() returns a new function that can be used in the comparison argument to compare_levels() to compute those contrasts.

Value

A function that takes a single argument, var, containing a variable to generate contrasts for (e.g., a factor or a character vector) and returns a function that generates a list of named unevaluated expressions representing different contrasts of that variable. This function is suitable to be used as the comparison argument in compare_levels().

Author(s)

Matthew Kay

See Also

compare_levels(), emmeans::contrast-methods. See gather_emmeans_draws() for a different approach to using emmeans with tidybayes.

Examples

library(dplyr)
library(ggplot2)

data(RankCorr, package = "ggdist")

# emmeans contrast methods return matrices. E.g. the "eff" comparison
# compares each level to the average of all levels:
emmeans:::eff.emmc(c("a","b","c","d"))

# tidybayes::compare_levels() can't use a contrast matrix like this
# directly; it takes arbitrary expressions of factor levels. But
# we can use `emmeans_comparison` to generate the equivalent expressions:
emmeans_comparison("eff")(c("a","b","c","d"))

# We can use the "eff" comparison type with `compare_levels()` as follows:
RankCorr %>%
  spread_draws(b[i,j]) %>%
  filter(j == 1) %>%
  compare_levels(b, by = i, comparison = emmeans_comparison("eff")) %>%
  median_qi()

Description

Extract draws from a Bayesian model for one or more variables (possibly with named dimensions) into one of two types of long-format data frames.

Usage

gather_draws(
  model,
  ...,
  regex = FALSE,
  sep = "[, ]",
  ndraws = NULL,
  seed = NULL,
  draw_indices = c(".chain", ".iteration", ".draw"),
  n
)

spread_draws(
  model,
  ...,
  regex = FALSE,
  sep = "[, ]",
  ndraws = NULL,
  seed = NULL,
  draw_indices = c(".chain", ".iteration", ".draw"),
  n
)

Arguments

Details

Imagine a JAGS or Stan fit named model. The model may contain a variable named b[i,v] (in the JAGS or Stan language) with dimension i in 1:100 and dimension v in 1:3. However, the default format for draws returned from JAGS or Stan in R will not reflect this indexing structure, instead they will have multiple columns with names like "b[1,1]", "b[2,1]", etc.

spread_draws and gather_draws provide a straightforward syntax to translate these columns back into properly-indexed variables in two different tidy data frame formats, optionally recovering dimension types (e.g. factor levels) as it does so.

spread_draws and gather_draws return data frames already grouped by all dimensions used on the variables you specify.

The difference between spread_draws is that names of variables in the model will be spread across the data frame as column names, whereas gather_draws will gather variables into a single column named ".variable" and place values of variables into a column named ".value". To use naming schemes from other packages (such as broom), consider passing results through functions like to_broom_names() or to_ggmcmc_names().

For example, spread_draws(model, a[i], b[i,v]) might return a grouped data frame (grouped by i and v), with:

• column ".chain": the chain number. NA if not applicable to the model type; this is typically only applicable to MCMC algorithms.

• column ".iteration": the iteration number. Guaranteed to be unique within-chain only. NA if not applicable to the model type; this is typically only applicable to MCMC algorithms.

• column ".draw": a unique number for each draw from the posterior. Order is not guaranteed to be meaningful.

• column "i": value in 1:5

• column "v": value in 1:10

• column "a": value of "a[i]" for draw ".draw"

• column "b": value of "b[i,v]" for draw ".draw"

gather_draws(model, a[i], b[i,v]) on the same model would return a grouped data frame (grouped by i and v), with:

• column ".chain": the chain number

• column ".iteration": the iteration number

• column ".draw": the draw number

• column "i": value in 1:5

• column "v": value in 1:10, or NA if ".variable" is "a".

• column ".variable": value in c("a", "b").

• column ".value": value of "a[i]" (when ".variable" is "a") or "b[i,v]" (when ".variable" is "b") for draw ".draw"

spread_draws and gather_draws can use type information applied to the model object by recover_types() to convert columns back into their original types. This is particularly helpful if some of the dimensions in your model were originally factors. For example, if the v dimension in the original data frame data was a factor with levels c("a","b","c"), then we could use recover_types before spread_draws:

model %>%
 recover_types(data) 
 spread_draws(model, b[i,v])

Which would return the same data frame as above, except the "v" column would be a value in c("a","b","c") instead of 1:3.

For variables that do not share the same subscripts (or share some but not all subscripts), we can supply their specifications separately. For example, if we have a variable d[i] with the same i subscript as b[i,v], and a variable x with no subscripts, we could do this:

spread_draws(model, x, d[i], b[i,v])

Which is roughly equivalent to this:

spread_draws(model, x) %>%
 inner_join(spread_draws(model, d[i])) %>%
 inner_join(spread_draws(model, b[i,v])) %>%
 group_by(i,v)

Similarly, this:

gather_draws(model, x, d[i], b[i,v])

Is roughly equivalent to this:

bind_rows(
 gather_draws(model, x),
 gather_draws(model, d[i]),
 gather_draws(model, b[i,v])
)

The c and cbind functions can be used to combine multiple variable names that have the same dimensions. For example, if we have several variables with the same subscripts i and v, we could do either of these:

spread_draws(model, c(w, x, y, z)[i,v])

spread_draws(model, cbind(w, x, y, z)[i,v])  # equivalent

Each of which is roughly equivalent to this:

spread_draws(model, w[i,v], x[i,v], y[i,v], z[i,v])

Besides being more compact, the c()-style syntax is currently also faster (though that may change).

Dimensions can be omitted from the resulting data frame by leaving their names blank; e.g. spread_draws(model, b[,v]) will omit the first dimension of b from the output. This is useful if a dimension is known to contain all the same value in a given model.

The shorthand .. can be used to specify one column that should be put into a wide format and whose names will be the base variable name, plus a dot ("."), plus the value of the dimension at ... For example:

spread_draws(model, b[i,..]) would return a grouped data frame (grouped by i), with:

• column ".chain": the chain number

• column ".iteration": the iteration number

• column ".draw": the draw number

• column "i": value in 1:20

• column "b.1": value of "b[i,1]" for draw ".draw"

• column "b.2": value of "b[i,2]" for draw ".draw"

• column "b.3": value of "b[i,3]" for draw ".draw"

An optional clause in the form ⁠| wide_dimension⁠ can also be used to put the data frame into a wide format based on wide_dimension. For example, this:

spread_draws(model, b[i,v] | v)

is roughly equivalent to this:

spread_draws(model, b[i,v]) %>% spread(v,b)

The main difference between using the | syntax instead of the .. syntax is that the | syntax respects prototypes applied to dimensions with recover_types(), and thus can be used to get columns with nicer names. For example:

model %>% recover_types(data) %>% spread_draws(b[i,v] | v)

would return a grouped data frame (grouped by i), with:

• column ".chain": the chain number

• column ".iteration": the iteration number

• column ".draw": the draw number

• column "i": value in 1:20

• column "a": value of "b[i,1]" for draw ".draw"

• column "b": value of "b[i,2]" for draw ".draw"

• column "c": value of "b[i,3]" for draw ".draw"

The shorthand . can be used to specify columns that should be nested into vectors, matrices, or n-dimensional arrays (depending on how many dimensions are specified with .).

For example, spread_draws(model, a[.], b[.,.]) might return a data frame, with:

• column ".chain": the chain number.

• column ".iteration": the iteration number.

• column ".draw": a unique number for each draw from the posterior.

• column "a": a list column of vectors.

• column "b": a list column of matrices.

Ragged arrays are turned into non-ragged arrays with missing entries given the value NA.

Finally, variable names can be regular expressions by setting regex = TRUE; e.g.:

spread_draws(model, `b_.*`[i], regex = TRUE)

Would return a tidy data frame with variables starting with b_ and having one dimension.

Value

A data frame.

Author(s)

Matthew Kay

See Also

spread_rvars(), recover_types(), compose_data().

Examples

library(dplyr)
library(ggplot2)

data(RankCorr, package = "ggdist")

RankCorr %>%
  spread_draws(b[i, j])

RankCorr %>%
  spread_draws(b[i, j], tau[i], u_tau[i])


RankCorr %>%
  gather_draws(b[i, j], tau[i], u_tau[i])

RankCorr %>%
  gather_draws(tau[i], typical_r) %>%
  median_qi()

Description

Extract draws from the result of a call to emmeans::emmeans() (formerly lsmeans) or emmeans::ref_grid() applied to a Bayesian model.

Usage

gather_emmeans_draws(object, value = ".value", ...)

## Default S3 method:
gather_emmeans_draws(object, value = ".value", ...)

## S3 method for class 'emm_list'
gather_emmeans_draws(object, value = ".value", grid = ".grid", ...)

Arguments

Details

emmeans::emmeans() provides a convenient syntax for generating draws from "estimated marginal means" from a model, and can be applied to various Bayesian models, like rstanarm::stanreg-objects and MCMCglmm::MCMCglmm(). Given a emmeans::ref_grid() object as returned by functions like emmeans::ref_grid() or emmeans::emmeans() applied to a Bayesian model, gather_emmeans_draws returns a tidy format data frame of draws from the marginal posterior distributions generated by emmeans::emmeans().

Value

A tidy data frame of draws. The columns of the reference grid are returned as-is, with an additional column called .value (by default) containing marginal draws. The resulting data frame is grouped by the columns from the reference grid to make use of summary functions like point_interval() straightforward.

If object is an emmeans::emm_list(), which contains estimates from different reference grids, an additional column with the default name of ".grid" is added to indicate the reference grid for each row in the output. The name of this column is controlled by the grid argument.

Author(s)

Matthew Kay

See Also

emmeans::emmeans()

Examples

## Not run: 

library(dplyr)
library(magrittr)
library(brms)
library(emmeans)

# Here's an example dataset with a categorical predictor (`condition`) with several levels:
set.seed(5)
n = 10
n_condition = 5
ABC = tibble(
  condition = rep(c("A","B","C","D","E"), n),
  response = rnorm(n * 5, c(0,1,2,1,-1), 0.5)
)

m = brm(response ~ condition, data = ABC,
  # 1 chain / few iterations just so example runs quickly
  # do not use in practice
  chains = 1, iter = 500)

# Once we've fit the model, we can use emmeans() (and functions
# from that package) to get whatever marginal distributions we want.
# For example, we can get marginal means by condition:
m %>%
  emmeans(~ condition) %>%
  gather_emmeans_draws() %>%
  median_qi()

# or we could get pairwise differences:
m %>%
  emmeans(~ condition) %>%
  contrast(method = "pairwise") %>%
  gather_emmeans_draws() %>%
  median_qi()

# see the documentation of emmeans() for more examples of types of
# contrasts supported by that packge.


## End(Not run)

Description

Fast method for producing combinations of values in a value column for different levels of a key column, assuming long-format (tidy) data with an equal number of values per key. Among other things, this is useful for producing scatter-plot matrices.

Usage

gather_pairs(
  data,
  key,
  value,
  row = ".row",
  col = ".col",
  x = ".x",
  y = ".y",
  triangle = c("lower only", "upper only", "lower", "upper", "both only", "both")
)

Arguments

Value

A tidy data frame of combinations of values in key and value, with columns row and col (default names ".row" and ".col") containing values from key, and columns y and x (default names ".y" and ".x") containing values from value.

Author(s)

Matthew Kay

See Also

emmeans::emmeans()

Examples

library(ggplot2)
library(dplyr)

t_a = rnorm(100)
t_b = rnorm(100, t_a * 2)
t_c = rnorm(100)

df = rbind(
  data.frame(g = "a", t = t_a),
  data.frame(g = "b", t = t_b),
  data.frame(g = "c", t = t_c)
)

df %>%
  gather_pairs(g, t, row = "g_row", col = "g_col", x = "t_x", y = "t_y") %>%
  ggplot(aes(t_x, t_y)) +
  geom_point() +
  facet_grid(vars(g_row), vars(g_col))

df %>%
  gather_pairs(g, t, triangle = "upper") %>%
  ggplot(aes(.x, .y)) +
  geom_point() +
  facet_grid(vars(.row), vars(.col))

df %>%
  gather_pairs(g, t, triangle = "both") %>%
  ggplot(aes(.x, .y)) +
  geom_point() +
  facet_grid(vars(.row), vars(.col))

data(line, package = "coda")

line %>%
  tidy_draws() %>%
  gather_variables() %>%
  gather_pairs(.variable, .value) %>%
  ggplot(aes(.x, .y)) +
  geom_point(alpha = .25) +
  facet_grid(vars(.row), vars(.col))

line %>%
  tidy_draws() %>%
  gather_variables() %>%
  gather_pairs(.variable, .value) %>%
  ggplot(aes(.x, .y, color = factor(.chain))) +
  geom_density_2d(alpha = .5) +
  facet_grid(vars(.row), vars(.col))

Description

Extract draws from a Bayesian model for one or more variables (possibly with named dimensions) into one of two types of long-format data frames of posterior::rvar objects.

Usage

gather_rvars(model, ..., ndraws = NULL, seed = NULL)

spread_rvars(model, ..., ndraws = NULL, seed = NULL)

Arguments

Details

Imagine a JAGS or Stan fit named model. The model may contain a variable named b[i,v] (in the JAGS or Stan language) with dimension i in 1:100 and dimension v in 1:3. However, the default format for draws returned from JAGS or Stan in R will not reflect this indexing structure, instead they will have multiple columns with names like "b[1,1]", "b[2,1]", etc.

spread_rvars and gather_rvars provide a straightforward syntax to translate these columns back into properly-indexed rvars in two different tidy data frame formats, optionally recovering dimension types (e.g. factor levels) as it does so.

spread_rvars will spread names of variables in the model across the data frame as column names, whereas gather_rvars will gather variable names into a single column named ".variable" and place values of variables into a column named ".value". To use naming schemes from other packages (such as broom), consider passing results through functions like to_broom_names() or to_ggmcmc_names().

For example, spread_rvars(model, a[i], b[i,v]) might return a data frame with:

• column "i": value in 1:5

• column "v": value in 1:10

• column "a": rvar containing draws from "a[i]"

• column "b": rvar containing draws from "b[i,v]"

gather_rvars(model, a[i], b[i,v]) on the same model would return a data frame with:

• column "i": value in 1:5

• column "v": value in 1:10, or NA on rows where ".variable" is "a".

• column ".variable": value in c("a", "b").

• column ".value": rvar containing draws from "a[i]" (when ".variable" is "a") or "b[i,v]" (when ".variable" is "b")

spread_rvars and gather_rvars can use type information applied to the model object by recover_types() to convert columns back into their original types. This is particularly helpful if some of the dimensions in your model were originally factors. For example, if the v dimension in the original data frame data was a factor with levels c("a","b","c"), then we could use recover_types before spread_rvars:

model %>%
 recover_types(data) 
 spread_rvars(model, b[i,v])

Which would return the same data frame as above, except the "v" column would be a value in c("a","b","c") instead of 1:3.

For variables that do not share the same subscripts (or share some but not all subscripts), we can supply their specifications separately. For example, if we have a variable d[i] with the same i subscript as b[i,v], and a variable x with no subscripts, we could do this:

spread_rvars(model, x, d[i], b[i,v])

Which is roughly equivalent to this:

spread_rvars(model, x) %>%
 inner_join(spread_rvars(model, d[i])) %>%
 inner_join(spread_rvars(model, b[i,v]))

Similarly, this:

gather_rvars(model, x, d[i], b[i,v])

Is roughly equivalent to this:

bind_rows(
 gather_rvars(model, x),
 gather_rvars(model, d[i]),
 gather_rvars(model, b[i,v])
)

The c and cbind functions can be used to combine multiple variable names that have the same dimensions. For example, if we have several variables with the same subscripts i and v, we could do either of these:

spread_rvars(model, c(w, x, y, z)[i,v])

spread_rvars(model, cbind(w, x, y, z)[i,v])  # equivalent

Each of which is roughly equivalent to this:

spread_rvars(model, w[i,v], x[i,v], y[i,v], z[i,v])

Besides being more compact, the c()-style syntax is currently also slightly faster (though that may change).

Dimensions can be left nested in the resulting rvar objects by leaving their names blank; e.g. spread_rvars(model, b[i,]) will place the first index (i) into rows of the data frame but leave the second index nested in the b column (see Examples below).

Value

A data frame.

Author(s)

Matthew Kay

See Also

spread_draws(), recover_types(), compose_data(). See also posterior::rvar() and posterior::as_draws_rvars(), the functions that power spread_rvars and gather_rvars.

Examples

library(dplyr)

data(RankCorr, package = "ggdist")

RankCorr %>%
  spread_rvars(b[i, j])

# leaving an index out nests the index in the column containing the rvar
RankCorr %>%
  spread_rvars(b[i, ])

RankCorr %>%
  spread_rvars(b[i, j], tau[i], u_tau[i])

# gather_rvars places variables and values in a longer format data frame
RankCorr %>%
  gather_rvars(b[i, j], tau[i], typical_r)

Description

Given a data frame such as might be returned by tidy_draws() or spread_draws(), gather variables and their values from that data frame into a ".variable" and ".value" column.

Usage

gather_variables(data, exclude = c(".chain", ".iteration", ".draw", ".row"))

Arguments

Details

This function gathers every column except grouping columns and those matching the expression exclude into key/value columns ".variable" and ".value".

Imagine a data frame data as returned by spread_draws(fit, a[i], b[i,v]), like this:

• column ".chain": the chain number

• column ".iteration": the iteration number

• column ".draw": the draw number

• column "i": value in 1:5

• column "v": value in 1:10

• column "a": value of "a[i]" for draw number ".draw"

• column "b": value of "b[i,v]" for draw number ".draw"

gather_variables(data) on that data frame would return a grouped data frame (grouped by i and v), with:

• column ".chain": the chain number

• column ".iteration": the iteration number

• column ".draw": the draw number

• column "i": value in 1:5

• column "v": value in 1:10

• column ".variable": value in c("a", "b").

• column ".value": value of "a[i]" (when ".variable" is "a"; repeated for every value of "v") or "b[i,v]" (when ".variable" is "b") for draw number ".draw"

In this example, this call:

gather_variables(data)

Is roughly equivalent to:

data %>%
  gather(.variable, .value, -c(.chain, .iteration, .draw, i, v)) %>%
  group_by(.variable, .add = TRUE)

Value

A data frame.

Author(s)

Matthew Kay

See Also

spread_draws(), tidy_draws().

Examples

library(dplyr)

data(RankCorr, package = "ggdist")

RankCorr %>%
  spread_draws(b[i,v], tau[i]) %>%
  gather_variables() %>%
  median_qi()

# the first three lines below are roughly equivalent to ggmcmc::ggs(RankCorr)
RankCorr %>%
  tidy_draws() %>%
  gather_variables() %>%
  median_qi()

Description

Get a character vector of the names of the variables in a variety of fitted Bayesian model types. All models supported by tidy_draws() are supported.

Usage

get_variables(model)

## Default S3 method:
get_variables(model)

## S3 method for class 'mcmc'
get_variables(model)

## S3 method for class 'mcmc.list'
get_variables(model)

Arguments

Details

This function is often useful for inspecting a model interactively in order to construct calls to spread_draws() or gather_draws() in order to extract draws from models in a tidy format.

Value

A character vector of variable names in the fitted model.

Author(s)

Matthew Kay

See Also

spread_draws(), gather_draws().

Examples

data(line, package = "coda")
get_variables(line)

data(RankCorr, package = "ggdist")
get_variables(RankCorr)

Description

Generates a function for generating names of index columns for factors in compose_data() by prefixing a character vector to the original column name.

Usage

n_prefix(prefix)

Arguments

See Also

The .n_name argument of compose_data().

Examples

library(magrittr)

df = data.frame(
  plot = factor(paste0("p", rep(1:8, times = 2))),
  site = factor(paste0("s", rep(1:4, each = 2, times = 2)))
)

# without changing `.n_name`, compose_data() will prefix indices
# with "n" by default
df %>%
  compose_data()

# you can use n_prefix() to define a different prefix (e.g. "N"):
df %>%
  compose_data(.n_name = n_prefix("N"))

Description

Converts between data-frame-of-rvars format and long-data-frame-of-draws formats by nesting or unnesting all columns containing posterior::rvar objects.

Usage

nest_rvars(data)

unnest_rvars(data)

Arguments

Value

For nest_rvars(), returns a data frame without .chain, .iteration, and .draw columns, where all non-grouped columns have been converted to rvars.

For unnest_rvars(), returns a data frame with .chain, .iteration, and .draw columns added, where every rvar column in the input has been converted to (one or more) columns containing draws from those rvars in long format. The result is grouped by all non-rvar columns in the input; this ensures that nest_rvars(unnest_rvars(x)) returns x.

Examples

library(dplyr)

data(RankCorr, package = "ggdist")

# here's a data frame with some rvars
rvar_df = RankCorr %>%
  spread_rvars(b[i,], tau[i])
rvar_df

# we can unnest it into long format.
# note how the result is grouped by all non-rvar input columns,
# and nested indices in `b` are converted into columns.
draws_df = rvar_df %>%
  unnest_rvars()
draws_df

# calling nest_rvars() again on the result of unnest_rvars()
# recovers the original data frame
nest_rvars(draws_df)

Description

Deprecated function for generating prediction curves (or a density for a prediction curve).

Usage

predict_curve(data, formula, summary = median, ...)

predict_curve_density(
  data,
  formula,
  summary = function(...) density_bins(..., n = n),
  n = 50,
  ...
)

Arguments

Details

This function is deprecated. Use modelr::data_grid() combined with point_interval() or dplyr::do() and density_bins() instead.

The function generates a predictive curve given posterior draws (data), an expression (formula), and a set of variables defining the curve (...). For every group in data (if it is a grouped data frame—see group_by(); otherwise the entire data frame is taken at once), and for each combination of values in ..., the right-hand side of formula is evaluated and its results passed to the summary function. This allows a predictive curve to be generated, given (e.g.) some samples of coefficients in data and a set of predictors defining the space of the curve in ....

Given a summary function like median() or mean(), this function will produce the median (resp. mean) prediction at each point on the curve.

Given a summary function like density_bins(), this function will produce a predictive distribution for each point on the curve. predict_curve_density is a shorthand for such a call, with a convenient argument for adjusting the number of bins per point on the curve.

Value

If formula is in the form lhs ~ rhs and summary is a function that returns a single value, such as median or mode, then predict_curve returns a data.frame with a column for each group in data (if it was grouped), a column for each variable in ..., and a column named lhs with the value of summary(rhs) evaluated for every group in data and combination of variables in ....

If summary is a function that returns a data.frame, such as density_bins(), predict_curve has the same set of columns as above, except that in place of the lhs column is a set of columns named lhs.x for every column named x returned by summary. For example, density_bins() returns a data frame with the columns mid, lower, upper, and density, so the data frame returned by predict_curve with summary = density_bins will have columns lhs.mid, lhs.lower, lhs.upper, and lhs.density in place of lhs.

Author(s)

Matthew Kay

See Also

See density_bins().

Examples

# Deprecated; see examples for density_bins

Description

Decorate a Bayesian model fit or a sample from it with types for variable and dimension data types. Meant to be used before calling spread_draws() or gather_draws() so that the values returned by those functions are translated back into useful data types.

Usage

recover_types(model, ...)

Arguments

Details

Each argument in ... specifies a list or data.frame. The model is decorated with a list of constructors that can convert a numeric column into the data types in the lists in ....

Then, when spread_draws() or gather_draws() is called on the decorated model, each list entry with the same name as the variable or a dimension in variable_spec is a used as a prototype for that variable or dimension — i.e., its type is taken to be the expected type of that variable or dimension. Those types are used to translate numeric values of variables back into useful values (for example, levels of a factor).

The most common use of recover_types is to automatically translate dimensions of a variable that correspond to levels of a factor in the original data back into levels of that factor. The simplest way to do this is to pass in the data frame from which the original data came.

Supported types of prototypes are factor, ordered, and logical. For example:

• if prototypes$v is a factor, the v column in the returned draws is translated into a factor using factor(v, labels=levels(prototypes$v), ordered=is.ordered(prototypes$v)).

• if prototypes$v is a logical, the v column is translated into a logical using as.logical(v).

Additional data types can be supported by providing a custom implementation of the generic function as_constructor.

Value

A decorated version of model.

Author(s)

Matthew Kay

See Also

spread_draws(), gather_draws(), compose_data().

Examples

## Not run: 

library(dplyr)
library(magrittr)
library(rstan)

# Here's an example dataset with a categorical predictor (`condition`) with several levels:
set.seed(5)
n = 10
n_condition = 5
ABC = tibble(
  condition = factor(rep(c("A","B","C","D","E"), n)),
  response = rnorm(n * 5, c(0,1,2,1,-1), 0.5)
)

# We'll fit the following model to it:
stan_code = "
  data {
    int<lower=1> n;
    int<lower=1> n_condition;
    int<lower=1, upper=n_condition> condition[n];
    real response[n];
  }
  parameters {
    real overall_mean;
    vector[n_condition] condition_zoffset;
    real<lower=0> response_sd;
    real<lower=0> condition_mean_sd;
  }
  transformed parameters {
    vector[n_condition] condition_mean;
    condition_mean = overall_mean + condition_zoffset * condition_mean_sd;
  }
  model {
    response_sd ~ cauchy(0, 1);       // => half-cauchy(0, 1)
    condition_mean_sd ~ cauchy(0, 1); // => half-cauchy(0, 1)
    overall_mean ~ normal(0, 5);

    //=> condition_mean ~ normal(overall_mean, condition_mean_sd)
    condition_zoffset ~ normal(0, 1);

    for (i in 1:n) {
      response[i] ~ normal(condition_mean[condition[i]], response_sd);
    }
  }
"

m = stan(model_code = stan_code, data = compose_data(ABC), control = list(adapt_delta=0.99),
  # 1 chain / few iterations just so example runs quickly
  # do not use in practice
  chains = 1, iter = 500)

# without using recover_types(), the `condition` column returned by spread_draws()
# will be an integer:
m %>%
  spread_draws(condition_mean[condition]) %>%
  median_qi()

# If we apply recover_types() first, subsequent calls to other tidybayes functions will
# automatically back-convert factors so that they are labeled with their original levels
# (assuming the same name is used)
m %<>% recover_types(ABC)

# now the `condition` column with be a factor with levels "A", "B", "C", ...
m %>%
  spread_draws(condition_mean[condition]) %>%
  median_qi()


## End(Not run)

Description

Given a tidy-format data frame of draws with a column indexing each draw, subsample the data frame to a given size based on a column indexing draws, ensuring that rows in sub-groups of a grouped data frame are sampled from the same draws.

Usage

sample_draws(data, ndraws, draw = ".draw", seed = NULL)

Arguments

Details

sample_draws() makes it easier to sub-sample a grouped, tidy-format data frame of draws. On a grouped data frame, the naive approach of using filter with the .draw column will give incorrect results as it will select a different sample within each group. sample_draws() ensures the same sample is selected within each group.

Author(s)

Matthew Kay

Examples

## Not run: 

library(ggplot2)
library(dplyr)
library(brms)
library(modelr)

theme_set(theme_light())

m_mpg = brm(mpg ~ hp * cyl, data = mtcars,
  # 1 chain / few iterations just so example runs quickly
  # do not use in practice
  chains = 1, iter = 500)

# draw 100 fit lines from the posterior and overplot them
mtcars %>%
  group_by(cyl) %>%
  data_grid(hp = seq_range(hp, n = 101)) %>%
  add_epred_draws(m_mpg) %>%
  # NOTE: only use sample_draws here when making spaghetti plots; for
  # plotting intervals it is always best to use all draws
  sample_draws(100) %>%
  ggplot(aes(x = hp, y = mpg, color = ordered(cyl))) +
  geom_line(aes(y = .epred, group = paste(cyl, .draw)), alpha = 0.25) +
  geom_point(data = mtcars)


## End(Not run)

Description

An implementation of posterior::summarise_draws() for grouped data frames (dplyr::grouped_df objects) such as returned by dplyr::group_by() and the various grouped-data-aware functions in tidybayes, such as spread_draws(), gather_draws(), add_epred_draws(), and add_predicted_draws(). This function provides a quick way to get a variety of summary statistics and diagnostics on draws.

Usage

## S3 method for class 'grouped_df'
summarise_draws(.x, ...)

Arguments

Details

While posterior::summarise_draws() can operate on tidy data frames of draws in the posterior::draws_df() format, that format does not support grouping columns. This provides an implementation of summarise_draws() that does support grouped data tables, essentially applying posterior::summarise_draws() to every sub-table of .x implied by the groups defined on the data frame.

See posterior::summarise_draws() for more details on the summary statistics and diagnostics you can use with this function. If you just want point summaries and intervals (not diagnostics), particularly for plotting, see point_interval(), which returns long-format data tables more suitable for that purpose (especially if you want to plot multiple uncertainty levels).

Value

A data frame (actually, a tibble) with all grouping columns from .x, a "variable" column containing variable names from .x, and the remaining columns containing summary statistics and diagnostics.

Author(s)

Matthew Kay

See Also

posterior::summarise_draws(), point_interval()

Examples

library(posterior)
library(dplyr)

d = posterior::example_draws()

# The default posterior::summarise_draws() summarises all variables without
# splitting out indices:
summarise_draws(d)

# The grouped_df implementation of summarise_draws() in tidybayes can handle
# output from spread_draws(), which is a grouped data table with the indices
# (here, `i`) left as columns:
d %>%
  spread_draws(theta[i]) %>%
  summarise_draws()

# Summary functions can also be provided, as in posterior::summarise_draws():
d %>%
  spread_draws(theta[i]) %>%
  summarise_draws(median, mad, rhat, ess_tail)

Description

Extract draws from a Bayesian fit into a wide-format data frame with a .chain, .iteration, and .draw column, as well as all variables as columns. This function does not parse indices from variable names (e.g. for variable names like "x[1]"); see spread_draws() or gather_draws() for functions that parse variable indices.

Usage

tidy_draws(model, ...)

## Default S3 method:
tidy_draws(model, ...)

## S3 method for class 'draws'
tidy_draws(model, ...)

## S3 method for class 'data.frame'
tidy_draws(model, ...)

## S3 method for class 'mcmc.list'
tidy_draws(model, ...)

## S3 method for class 'stanfit'
tidy_draws(model, ...)

## S3 method for class 'stanreg'
tidy_draws(model, ...)

## S3 method for class 'runjags'
tidy_draws(model, ...)

## S3 method for class 'jagsUI'
tidy_draws(model, ...)

## S3 method for class 'brmsfit'
tidy_draws(model, ...)

## S3 method for class 'CmdStanFit'
tidy_draws(model, ...)

## S3 method for class 'CmdStanMCMC'
tidy_draws(model, ...)

## S3 method for class 'matrix'
tidy_draws(model, ...)

## S3 method for class 'MCMCglmm'
tidy_draws(model, ...)

Arguments

Details

This function can be useful for quick glances at models (especially combined with gather_variables() and median_qi()), and for models with parameters without indices in their names (like "x[1]"). spread_draws() and gather_draws(), which do parse variable name indices, call this function internally if their input is not already a tidy data frame.

To provide support for new models in tidybayes, you must provide an implementation of this function or an implementation of coda::as.mcmc.list() (tidy_draws should work on any model with an implementation of coda::as.mcmc.list())

tidy_draws() can be applied to a data frame that is already a tidy-format data frame of draws, provided it has one row per draw. In other words, it can be applied to data frames that have the same format it returns, and it will return the same data frame back, while checking to ensure the .chain, .iteration, and .draw columns are all integers (converting if possible) and that the .draw column is unique. This allows you to pass already-tidy-format data frames into other tidybayes functions, like spread_draws() or gather_draws(). This functionality can be useful if the tidying step is expensive: you can tidy once, possibly subsetting to some particular variables of interest, then call spread_draws() or gather_draws() repeatedly to extract variables and indices from the already-tidied data frame.

Value

A data frame (actually, a tibble) with a .chain column, .iteration column, .draw column, and one column for every variable in model.

Author(s)

Matthew Kay

See Also

spread_draws() or gather_draws(), which use this function internally and provides a friendly interface for extracting tidy data frames from model fits.

Examples

library(magrittr)

data(line, package = "coda")

line %>%
  tidy_draws()

Description

Deprecated functions, arguments, and column names and their alternatives are listed below. Many of the deprecations are due to a naming scheme overhaul in tidybayes version 1.0 (see Deprecated Functions and Deprecated Arguments and Column Names below) or due to the deprecation of horizontal shortcut geoms and stats in tidybayes 2.1 (see Deprecated Horizontal Shortcut Geoms and Stats).

Deprecated Functions

Several deprecated versions of functions use slightly different output formats (e.g., they use names like term and estimate where new functions use .variable and .value; or they set .iteration even when iteration information is not available — new functions always set .draw but may not set .iteration), so be careful when upgrading to new function names. See Deprecated Arguments and Column Names, below, for more information.

Functions deprecated in tidybayes 3.0:

• fitted_draws and add_fitted_draws are deprecated because their names were confusing: it was unclear to many users if these functions returned draws from the posterior predictive, the mean of the posterior predictive, or the linear predictor (and depending on model type it might have been either of the latter). Use epred_draws()/add_epred_draws() if you want the expectation of the posterior predictive and use linpred_draws()/add_linpred_draws() if you want the linear predictor.

Functions deprecated in tidybayes 1.0:

• spread_samples, extract_samples, and tidy_samples are deprecated names for spread_draws(). The spread/gather terminology better distinguishes the resulting data frame format, and draws is more correct terminology than samples for describing multiple realizations from a posterior distribution.

• gather_samples is a deprecated name for gather_draws(), reflecting a package-wide move to using draws instead of samples for describing multiple realizations from a distribution.

• unspread_samples is a deprecated name for unspread_draws(), reflecting a package-wide move to using draws instead of samples for describing multiple realizations from a distribution.

• ungather_samples is a deprecated name for ungather_draws(), reflecting a package-wide move to using draws instead of samples for describing multiple realizations from a distribution.

• fitted_samples / add_fitted_samples are deprecated names for fitted_draws / add_fitted_draws, reflecting a package-wide move to using draws instead of samples for describing multiple realizations from a distribution. (though see the note above about the deprecation of fitted_draws in favor of epred_draws() and linpred_draws()).

• predicted_samples / add_predicted_samples are deprecated names for predicted_draws() / add_predicted_draws(), reflecting a package-wide move to using draws instead of samples for describing multiple realizations from a distribution.

• gather_lsmeans_samples and gather_emmeans_samples are deprecated aliases for gather_emmeans_draws(). The new name (estimated marginal means) is more appropriate for Bayesian models than the old name (least-squares means), and reflects the naming of the newer emmeans package. It also reflects a package-wide move to using draws instead of samples for describing multiple realizations from a distribution.

• as_sample_tibble and as_sample_data_frame are deprecated aliases for tidy_draws(). The original intent of as_sample_tibble was to be used primarily internally (hence its less user-friendly name); however, increasingly I have come across use cases of tidy_draws that warrant a more user-friendly name. It also reflects a package-wide move to using draws instead of samples for describing multiple realizations from a distribution.

• ggeye is deprecated: for a package whose goal is flexible and customizable visualization, monolithic functions are inflexible and do not sufficiently capitalize on users' existing knowledge of ggplot; instead, I think it is more flexible to design geoms and stats that can used within a complete ggplot workflow. stat_eye() offers a horizontal eye plot geom that can be used instead of ggeye.

• See the sections below for additional deprecated functions, including horizontal geoms, stats, and point_intervals

Deprecated Eye Geom Spellings

geom_eye, geom_eyeh, and geom_halfeyeh are deprecated spellings of stat_eye() and stat_halfeye() from before name standardization of stats and geoms. Use those functions instead.

Deprecated Horizontal Shortcut Geoms and Stats

Due to the introduction of automatic orientation detection in tidybayes 2.1, shortcut geoms and stats (which end in h) are no longer necessary, and are deprecated. In most cases, these can simply be replaced with the same geom without the h suffix and they will remain horizontal; e.g. stat_halfeyeh(...) can simply be replaced with stat_halfeye(...). If automatic orientation detection fails, override it with the orientation parameter; e.g. stat_halfeye(orientation = "horizontal").

These deprecated stats and geoms include:

• stat_eyeh / stat_dist_eyeh

• stat_halfeyeh / stat_dist_halfeyeh

• geom_slabh / stat_slabh / stat_dist_slabh

• geom_intervalh / stat_intervalh / stat_dist_intervalh

• geom_pointintervalh / stat_pointintervalh / stat_dist_pointintervalh

• stat_gradientintervalh / stat_dist_gradientintervalh

• stat_cdfintervalh / stat_dist_cdfintervalh

• stat_ccdfintervalh / stat_dist_ccdfintervalh

• geom_dotsh / stat_dotsh / stat_dist_dotsh

• geom_dotsintervalh / stat_intervalh / stat_dist_intervalh

• stat_histintervalh

Deprecated Horizontal Point/Interval Functions

These functions ending in h (e.g., point_intervalh, median_qih) used to be needed for use with ggstance::stat_summaryh, but are no longer necessary because ggplot2::stat_summary() supports automatic orientation detection, so they have been deprecated. They behave identically to the corresponding function without the h, except that when passed a vector, they return a data frame with x/xmin/xmax instead of y/ymin/ymax.

• point_intervalh

• mean_qih / median_qih / mode_qih

• mean_hdih / median_hdih / mode_hdih

• mean_hdcih / median_hdcih / mode_hdcih

Deprecated Arguments and Column Names

Arguments deprecated in tidybayes 3.0 are:

• The n argument is now called ndraws in predicted_draws(), linpred_draws(), etc. This prevents some bugs due to partial matching of argument names where n might be mistaken for newdata.

• The value argument in linpred_draws() is now spelled linpred and defaults to ".linpred" in the same way that the predicted_draws() and epred_draws() functions work.

• The scale argument in linpred_draws() is no longer allowed (use transform instead) as this naming scheme only made sense when linpred_draws() was an alias for fitted_draws(), which it no longer is (see note above about the deprecation of fitted_draws()).

Versions of tidybayes before version 1.0 used a different naming scheme for several arguments and output columns.

Arguments and column names deprecated in tidybayes 1.0 are:

• term is now .variable

• estimate is now .value

• pred is now .prediction

• conf.low is now .lower

• conf.high is now .upper

• .prob is now .width

• The .draw column was added, and should be used instead of .chain and .iteration to uniquely identify draws when you do not care about chains. (.chain and .iteration are still provided for identifying draws within chains, if desired).

To translate to/from the old naming scheme in output, use to_broom_names() and from_broom_names().

Many of these names were updated in version 1.0 in order to make terminology more consistent and in order to satisfy these criteria:

• Ignore compatibility with broom names on the assumption an adapter function can be created.

• Use names that could be compatible with frequentist approaches (hence .width instead of .prob).

• Always precede with "." to avoid collisions with variable names in models.

• No abbreviations (remembering if something is abbreviated or not can be a pain).

• No two-word names (multi-word names can always be standardized on and used in documentation, but I think data frame output should be succinct).

• Names should be nouns (I made an exception for lower/upper because they are common).

Author(s)

Matthew Kay

Description

Tidybayes supports two classes of models and sample formats: Models/formats that provide prediction functions, and those that do not.

All Supported Models/Sample Formats

All supported models/formats support the base tidybayes sample extraction functions, such as tidy_draws(), spread_draws(), gather_draws(), spread_rvars(), and gather_rvars(). These models/formats include:

• rstan models

• cmdstanr models

• brms::brm() models

• rstanarm models

• runjags::runjags() models

• rjags::jags.model() models, if sampled using rjags::coda.samples()

• jagsUI::jags() models

• MCMCglmm::MCMCglmm() models

• coda::mcmc() and coda::mcmc.list() objects, which are output by several model types.

• posterior::draws objects

• Any object with an implementation of posterior::as_draws_df() or posterior::as_draws(). For a list of those available in your environment, run methods(as_draws_df) or methods(as_draws)

• Any object with an implementation of coda::as.mcmc.list(). For a list of those available in your environment, run methods(as.mcmc.list)

If you install the tidybayes.rethinking package, models from the rethinking package are also supported.

Models Supporting Prediction

In addition, the following models support fit and prediction extraction functions, such as add_epred_draws(), add_predicted_draws(), add_linpred_draws(), add_epred_rvars(), add_predicted_rvars(), and add_linpred_rvars():

• brms::brm() models

• rstanarm models

• any package with implementations of rstantools::posterior_epred(), rstantools::posterior_predict(), or rstantools::posterior_linpred() that include an argument called newdata which takes a data frame of predictors.

If your model type is not in the above list, you may still be able to use the add_draws() function to turn matrices of predictive draws (or fit draws) into tidy data frames. Or, you can wrap output from a prediction function in posterior::rvar() and add it to a data frame so long as that output is a matrix with draws as rows.

If you install the tidybayes.rethinking package, models from the rethinking package are also supported.

Extending tidybayes

To include basic support for new models, one need only implement the tidy_draws() generic function for that model. Alternatively, objects that support posterior::as_draws() or coda::as.mcmc.list() will automatically be supported by tidy_draws().

To include support for estimation and prediction, one must either implement the epred_draws(), predicted_draws(), and linpred_draws() functions or their correspond functions from rstantools: rstantools::posterior_epred(), rstantools::posterior_predict(), and rstantools::posterior_linpred(). If you take the latter approach, you should include newdata and ndraws arguments that work as documented in predicted_draws().

Description

Inverse operations of spread_draws() and gather_draws(), giving results that look like tidy_draws().

Usage

ungather_draws(
  data,
  ...,
  variable = ".variable",
  value = ".value",
  draw_indices = c(".chain", ".iteration", ".draw"),
  drop_indices = FALSE
)

unspread_draws(
  data,
  ...,
  draw_indices = c(".chain", ".iteration", ".draw"),
  drop_indices = FALSE
)

Arguments

Details

These functions take symbolic specifications of variable names and dimensions in the same format as spread_draws() and gather_draws() and invert the tidy data frame back into a data frame whose column names are variables with dimensions in them.

Value

A data frame.

Author(s)

Matthew Kay

See Also

spread_draws(), gather_draws(), tidy_draws().

Examples

library(dplyr)

data(RankCorr, package = "ggdist")

# We can use unspread_draws to allow us to manipulate draws with tidybayes
# and then transform the draws into a form we can use with packages like bayesplot.
# Here we subset b[i,j] to just values of i in 1:2 and j == 1, then plot with bayesplot
RankCorr %>%
  spread_draws(b[i,j]) %>%
  filter(i %in% 1:2, j == 1) %>%
  unspread_draws(b[i,j], drop_indices = TRUE) %>%
  bayesplot::mcmc_areas()

# As another example, we could use compare_levels to plot all pairwise comparisons
# of b[1,j] for j in 1:3
RankCorr %>%
  spread_draws(b[i,j]) %>%
  filter(i == 1, j %in% 1:3) %>%
  compare_levels(b, by = j) %>%
  unspread_draws(b[j], drop_indices = TRUE) %>%
  bayesplot::mcmc_areas()

Description

Generates a lookup vector such that x_at_y(x, y)[y] == x. Particularly useful for generating lookup tables for nested indices in conjunction with compose_data().

Usage

x_at_y(x, y, missing = NA)

Arguments

Details

x_at_y(x, y) returns a vector k such that k[y] == x. It also fills in missing values in y: if y is an integer, k will contain entries for all values from 1 to max(y); if y is a factor, k will contain entries for all values from 1 to nlevels(y). Missing values are replaced with missing (default NA).

Author(s)

Matthew Kay

See Also

compose_data().

Examples

library(magrittr)

df = data.frame(
  plot = factor(paste0("p", rep(1:8, times = 2))),
  site = factor(paste0("s", rep(1:4, each = 2, times = 2)))
)

# turns site into a nested index: site[p] gives the site for plot p
df %>%
  compose_data(site = x_at_y(site, plot))