ggplot - use pie chart to visualize number of items in each group in terms of percentages - R

Question

I want to create two pie chart to show number of people in each level of the factor variable. However, I want to obtain two pie charts, one for two groups.

Here is an example:

library(ggplot2)
library(dplyr)

df <- filter(diamonds, color %in% c("E", "D"))

ggplot(df,aes(x= "", fill=cut)) + 
  geom_bar()+
  facet_wrap(~color)+
  ggtitle(" ") +
  coord_polar("y", start=0)

How can I Express the count of items per each group (cut) per each facet (color) as percentage? So on the end I would obtain two full pie charts with the precentages written inside the pie chart.

Answer 1

It is probably easiest to transform the data before you plot the graph. If we want to find the percentage of values within each group, we could use this answer:

df <- df %>%
  group_by(color, cut) %>%
  summarise(count = n()) %>%
  group_by(color) %>%
  mutate(per=count/sum(count)) %>% 
  ungroup()

df
# A tibble: 10 x 4
   color cut       count    per
   <ord> <ord>     <int>  <dbl>
 1 D     Fair        163 0.0241
 2 D     Good        662 0.0977
 3 D     Very Good  1513 0.223 
 4 D     Premium    1603 0.237 
 5 D     Ideal      2834 0.418 
 6 E     Fair        224 0.0229
 7 E     Good        933 0.0952
 8 E     Very Good  2400 0.245 
 9 E     Premium    2337 0.239 
10 E     Ideal      3903 0.398 

We can change the labels of the ggplot to percentage as below:

ggplot(df, aes(x= "", y = per, fill=cut)) + 
  geom_col() +
  facet_wrap(~color)+
  ggtitle(" ") +
  coord_polar("y", start=0) +
  scale_y_continuous(labels = scales::percent)