R: Calculate and display percentages using dplyr and geom_text



df <- data.frame(Language = factor(c(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2), levels = 1:2, labels = c("GER", "ENG")),
                 Agegrp =   factor(c(1, 2, 3, 1, 2, 4, 1, 2, 3, 2, 3, 3, 3, 3, 1, 1, 2, 1, 1, 4), levels = c( 1, 2, 3, 4), labels = c("10-19", "20-29", "30-39", "40+")) 
                 ) 
  

df %>% ggplot(aes(x = Agegrp, fill = Language)) + 
  geom_bar(position = 'dodge') +
  labs(title = "Age-structure between German and English",
       y = "Number of persons")

Using the above sample data I can create the following plot. But

how can I calculate the percentages of each agegroup within each language (using dplyr) and
how can I do the same plot with percentages (y-axis should be percentages)?

In this example the percentages are very easy to see as both languages have the same number of cases (10) but this does not necessarily have to be the case with real data. Thank you for help!

Solution

To calculate percentage of each Agegrp within a Language you can try -

library(dplyr)
library(ggplot2)

df %>%
  count(Agegrp, Language) %>%
  group_by(Language) %>%
  mutate(n = prop.table(n)) %>%
  ungroup %>%
  ggplot(aes(x = Agegrp, y = n, fill = Language)) + 
  geom_col(position = 'dodge') +
  scale_y_continuous(labels = scales::percent) + 
  labs(title = "Age-structure between German and English",
       y = "Percentage of persons")