side-by-side barplot with ggplot

Question

I\'m trying to display a side-by-side bar plot that compares the counts of each a letter grade between the 2 columns. (A\'s next to each other, B\'s next to each other etc.)

Answer 1

You need to transform the data frame in a tidy form. For that you could use the tidyr package function gather. To ensure the correct sorting for the letter grade using an ordered factor is appropriate:

library(tidyr)
library(ggplot2)

dat <- data.frame(grade1 = c('A','A','A','B','B','C'), grade2 = c('A','B','C','C','D','D'))

tidy_dat <- gather(dat)
tidy_dat[,2] <- ordered(tidy_dat[,2], levels = c('A','B','C','D'))

ggplot(tidy_dat, aes(x= value, fill = key))+
   geom_bar(position = 'dodge')