ggplot geom_boxplot color and group variables

Question

I'm trying to make a straightforward boxplot in ggplot. I'm not sure how get a grouping variable and a color/fill variable. I've tried to gather, but that doesn't seem to work. Any thoughts?

library(tidyverse)
# Does not work
mtcars %>% 
  as_tibble() %>% 
  ggplot(aes(factor(gear), 
             mpg, 
             group = vs)) +
  geom_boxplot(aes(fill = as.factor(gear)))


# Does not work either
mtcars %>% 
  as_tibble() %>% 
  select(gear, mpg, vs) %>% 
  gather(key, value, -vs) %>% 
  ggplot(aes(key, 
             value)) +
  geom_boxplot(aes(color = vs))

Answer 1

I'm not sure this is your intended output ( gear as x-axis and fill ), but here's a working example:

mtcars %>%
  ggplot(
    aes(
      x = factor(gear),
      y = mpg,
      color = factor(vs),
      fill = factor(gear)
    )
  ) + geom_boxplot()

I've found being explicit when declaring your aesthetic mappings can be helpful when learning ggplot2 .

Answer 2

Alternatively:

mtcars %>% 
  as_tibble() %>% 
  group_by(vs) %>% 
  ggplot(aes(factor(gear), 
             mpg, 
             fill=as.factor(gear))) +
  geom_boxplot()