Add `gather_emmeans_rvars()`

[mattansb]

Although easy to generate a data frame with rvars from {emmeans} (similar to what's possible with marginaleffects::posterior_draws()), it would be nice to have this option built in - it will fit nicely with the other *_rvars() alternatives to the *_draws() functions.

library(dplyr)
library(brms)
library(emmeans)
library(tidybayes)

set.seed(5)
n <- 10
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,
         chains = 1, iter = 500)


eml <- emmeans(m, pairwise ~ condition)


gather_emmeans_draws(eml)
#> # A tibble: 3,750 × 7
#> # Groups:   condition, contrast, .grid [15]
#>    .grid   condition .chain .iteration .draw   .value contrast
#>    <chr>   <chr>      <int>      <int> <int>    <dbl> <chr>   
#>  1 emmeans A             NA         NA     1 -0.271   NA      
#>  2 emmeans A             NA         NA     2 -0.00172 NA      
#>  3 emmeans A             NA         NA     3 -0.167   NA      
#>  4 emmeans A             NA         NA     4  0.0142  NA      
#>  5 emmeans A             NA         NA     5  0.0934  NA      
#>  6 emmeans A             NA         NA     6 -0.0276  NA      
#>  7 emmeans A             NA         NA     7 -0.0110  NA      
#>  8 emmeans A             NA         NA     8  0.249   NA      
#>  9 emmeans A             NA         NA     9  0.162   NA      
#> 10 emmeans A             NA         NA    10  0.165   NA      
#> # ℹ 3,740 more rows
#> # ℹ Use `print(n = ...)` to see more rows


gather_emmeans_rvars <- function(object, ...) {
  tidybayes::nest_rvars(tidybayes::gather_emmeans_draws(object))
}

gather_emmeans_rvars(em_condition)
#> # A tibble: 15 × 4
#> # Groups:   condition, contrast, .grid [15]
#>    condition contrast .grid              .value
#>    <chr>     <chr>    <chr>          <rvar[1d]>
#>  1 A         NA       emmeans     0.1914 ± 0.18
#>  2 B         NA       emmeans     1.0134 ± 0.18
#>  3 C         NA       emmeans     1.8733 ± 0.18
#>  4 D         NA       emmeans     1.0220 ± 0.18
#>  5 E         NA       emmeans    -0.9509 ± 0.17
#>  6 NA        A - B    contrasts  -0.8220 ± 0.27
#>  7 NA        A - C    contrasts  -1.6819 ± 0.26
#>  8 NA        A - D    contrasts  -0.8306 ± 0.24
#>  9 NA        A - E    contrasts   1.1423 ± 0.25
#> 10 NA        B - C    contrasts  -0.8600 ± 0.25
#> 11 NA        B - D    contrasts  -0.0086 ± 0.26
#> 12 NA        B - E    contrasts   1.9643 ± 0.24
#> 13 NA        C - D    contrasts   0.8514 ± 0.25
#> 14 NA        C - E    contrasts   2.8242 ± 0.25
#> 15 NA        D - E    contrasts   1.9729 ± 0.26