Zoidie Zoidie - 1 month ago 6
R Question

change thickness median line geom_boxplot()

I want to do some modifications of a geom_boxplot(). Because my boxplots are really "small" sometimes (see yellow and green clade in the graphic here) i want to highlight the median even more. so is it possible to adjust the thickness of the median line?

Answer

This solution is not obvious from the documentation, but luckily does not require us to edit the source code of ggplot2. After digging through the source of ggplot2 I found that the thickness of the median line is controlled by the fatten parameter. By default fatten has a value of two:

require(reshape)
require(ggplot2)
cars_melt = melt(cars)

ggplot(aes(x = variable, y = value), data = cars_melt) + 
  geom_boxplot(fatten = 2) 

enter image description here

But if we increase the value to for example 4, the median line becomes thicker.

ggplot(aes(x = variable, y = value), data = cars_melt) + 
  geom_boxplot(fatten = 4) 

enter image description here