tidybayes (version 3.0.7)

emmeans_comparison: Use emmeans contrast methods with compare_levels

Description

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

Usage

emmeans_comparison(method, ...)

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().

Arguments

method

An emmeans-style contrast method. One of: (1) a string specifying the name of an emmeans contrast method, like "pairwise", "trt.vs.ctrl", "eff"; or (2) an emmeans-style contrast function itself, like emmeans::pairwise.emmc, emmeans::trt.vs.ctrl.emmc, etc, or a custom function that takes a vector of factor levels and returns a contrast matrix.

...

Arguments passed on to the contrast method.

Author

Matthew Kay

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.

See Also

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

Examples

if (FALSE) { # requireNamespace("emmeans", quietly = TRUE)

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()
}