Align violin plots with dodged box plots

Question

I have this data frame

set.seed(1234)
x <- rnorm(80, 5, 1)
df <- data.frame(groups = c(rep("group1",20),
                           rep("group2",20),
                           rep("group3",20),
                           rep("group4",20)),
                    value = x,
                    type = c(rep("A", 10),
                           rep("B", 10),
                           rep("A", 10),
                           rep("B", 10),
                           rep("A", 10),
                           rep("B", 10),
                           rep("A", 10),
                           rep("B", 10)))

And I would like to plot it as violin plot, aligned with a narrow box plot and grouped by 'type':

ggplot(data = df, aes(x = groups, y = value, fill = type)) +
  geom_violin()+
  geom_boxplot(width = 0.1, outlier.colour = NA)

However, the box plots does not align to the violin plots. What is the missing argument to tell ggplot to do such overlying?

Thanks!

Solution

You need to set the width of the dodging explicitly for both geoms:

dodge <- position_dodge(width = 0.4)

ggplot(data = df, aes(x = groups, y = value, fill = type)) +
  geom_violin(position = dodge)+
  geom_boxplot(width=.1, outlier.colour=NA, position = dodge) 

---

For a more thorough explanation, see What is the width argument in position_dodge?

Comments

[Roland]

I'm not sure what you mean exactly by "align". Possibly set the position? See help("position_dodge").

[svavil]

I'm looking for a way to make boxplots filled with white, while simultaneously retaining positions of both boxplots and violins, and keeping violins colored. Do you know a way to reach this?

[Henrik]

@svavil Yes, in geom_boxplot, use the group argument instead of fill. ggplot(data = df, aes(x = groups, y = value)) + geom_violin(aes(fill = type), position = dodge) + geom_boxplot(aes(group = interaction(type, groups)), width=.1, outlier.colour=NA, position = dodge). See ?aes_group_order.