How do I plot multiple Y boxes for each X variable in ggplot2?

Question

Here's a sample of my data df

group   score1  score2
a   12  15
a   11  14
a   24  22
b   34  24
b   14  23
b   33  44
c   11  22
c   23  34
c   32  43
...

I know how to use ggplot2 to make a boxplot comparing group with score1 and another boxplot comparing group with score2.

But how do I make one boxplot where X axis is group, with boxes for both score1 and score2?

Answer 1

I believe this is probably what you're getting at -- first you might want to consider tidying the dataset with tidyr, then you can make the plot using a call to interaction():

library(ggplot2)
library(tidyr)

df <- gather(df, score, value, -group)
head(df)
#   group  score value
# 1     a score1    12
# 2     a score1    11
# 3     a score1    24
# 4     b score1    34
# 5     b score1    14
# 6     b score1    33

ggplot(df, aes(x = interaction(score, group), y = value)) +
  geom_boxplot()

As an alternative, you could pass the new score variable to a color aesthetic to get something like this: