r - 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!

Answer 1

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) 

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