Use emmeans contrast methods with compare_levels
Convert emmeans contrast methods into comparison functions
suitable for use with compare_levels().
emmeans_comparison(method, ...)
method |
An emmeans-style contrast method. One of: (1) a string specifying
the name of an emmeans contrast method, like
|
... |
Arguments passed on to the contrast method. |
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.
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().
Matthew Kay
compare_levels(), emmeans::contrast-methods.
See gather_emmeans_draws() for a different approach to using emmeans with
tidybayes.
if (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:
print(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:
print(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()
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