Sort a grouping variable by a second numeric variable, in the presence of a faceting variable

sorting_vars.R

# Sort a grouping variable by a second numeric variable, in the presence of a faceting variable
# Ostensibly so that the grouping variable plots in ascending (or descending) order of the
# central tendency of the numeric variable.

library(tidyverse)

# Create a dataset
set.seed(10001)
my_df <- tibble(facet_var = rep(letters[1:4], each = 5*10),
                group_var = rep(rep(letters[13:17], each = 10), times = 4),
                group_shift = rep(rep(runif(5, min = 1, max = 5), each = 10), times = 4),
                value = runif(4*5*10, min = 20, max = 40) + group_shift)
set.seed(NULL)

# Sort the grouping variable
# This approach entirely within tidyverse
my_df <- my_df %>% 
  mutate(group_var = as.factor(group_var)) %>% 
  group_by(facet_var) %>% 
  mutate(group_var = fct_reorder(.f = group_var, .x = value,.fun = median))

# And plot
my_df %>% 
  ggplot(aes(x = group_var, y = value, color = group_var)) +
  geom_boxplot() +
  facet_wrap(.~facet_var)