ggplot2: Adding sample size information to x-axis tick labels

Question

This question is related to Create custom geom to compute summary statistics and display them *outside* the plotting region (NOTE: All functions have been simplified; no error

Answer 1

My solution might be a little simple but it works well.

Given an example with faceting by am I start by creating labels using paste and \n.

mtcars2 <- mtcars %>% 
  group_by(cyl, am) %>% mutate(n = n()) %>% 
  mutate(label = paste0(cyl,'\nN = ',n))

I then use these labels instead of cyl in the ggplot code

ggplot(mtcars2,
   aes(x = factor(label), y = mpg, color = factor(label))) + 
  geom_point() + 
  xlab('cyl') + 
  facet_wrap(~am, scales = 'free_x') +
  theme(legend.position = "none")

To produce something like the figure below.