Adding "Overall" group to facet_wrap (ggplot2)

Question

I have two groups in my data, A1 and A2. Each group has about 50% men and an approximately normal distribution of age. I want to plot a histogram of age distribution in each group, by gender, and an overall age distribution by gender (and maybe a genderless one too?).

Is there a way to do this with facet_wrap? If not, is there a way I can manipulate my data (e.g. add a dummy variable) and add this?

Answer 1

Suppose you have:

library(tidyverse)
ggplot(iris, 
       aes(Sepal.Length, fill = Sepal.Width > 3)) + 
  geom_histogram() +
  facet_wrap(~Species)

You could manipulate your data to include another copy of the dataset where Species is always "total." Then geom_histogram will use the full dataset for the facet corresponding to "total."

ggplot(iris %>%
         bind_rows(iris %>% mutate(Species = "total")), 
       aes(Sepal.Length, fill = Sepal.Width > 3)) + 
  geom_histogram() +
  # I want 'total' at the end
  facet_wrap(~fct_relevel(Species, "total", after = Inf), nrow = 1)