ggplot在使用`facet_wrap`时添加正态分布

A while I ago I sort of automated this drawing of theoretical densities with a function that I put in the ggh4x package I wrote, which you might find convenient. You would just have to make sure that the histogram and theoretical density are at the same scale (for example counts per x-axis unit).

library(palmerpenguins)
library(tidyverse)
library(ggh4x) # devtools::install_github("teunbrand/ggh4x")

penguins %>% 
  ggplot(aes(x=bill_length_mm, fill = species)) +
  geom_histogram(binwidth = 1) + 
  stat_theodensity(aes(y = after_stat(count))) +
  facet_wrap(~species)
#> Warning: Removed 2 rows containing non-finite values (stat_bin).

You can vary the bin size of the histogram, but you'd have to adjust the theoretical density count too. Typically you'd multiply by the binwidth.

penguins %>% 
  ggplot(aes(x=bill_length_mm, fill = species)) +
  geom_histogram(binwidth = 2) + 
  stat_theodensity(aes(y = after_stat(count)*2)) +
  facet_wrap(~species)
#> Warning: Removed 2 rows containing non-finite values (stat_bin).

^{Created on 2021-01-27 by the reprex package (v0.3.0)}

如果这太麻烦了，您总是可以将直方图转换为密度，而不是将密度转换为计数。

penguins %>% 
  ggplot(aes(x=bill_length_mm, fill = species)) +
  geom_histogram(aes(y = after_stat(density))) + 
  stat_theodensity() +
  facet_wrap(~species)