Expression in ggplot2 facet labels

10
votes

I would like to have an R expression in a ggplot2 facet label.

Let's say I'm plotting the tips data.frame:

library(reshape2)
> head(tips)
  total_bill  tip    sex smoker day   time size
1      16.99 1.01 Female     No Sun Dinner    2
2      10.34 1.66   Male     No Sun Dinner    3
3      21.01 3.50   Male     No Sun Dinner    3
4      23.68 3.31   Male     No Sun Dinner    2
5      24.59 3.61 Female     No Sun Dinner    4
6      25.29 4.71   Male     No Sun Dinner    4

as follows:

library(ggplot2)
sp <- ggplot(tips, aes(x=total_bill, y=tip/total_bill)) + 
         geom_point(shape=1) + 
         facet_wrap(~sex, ncol = 1)

enter image description here

Instead of having "Female" and "Male" as facet labels I would like to have: "Female subjects" and "Male subjects", respectively. As far as I know italicizing a label in R is achieved through the expression function, but I don't know how to combine that with facet_wrap.

3
rggplot2labelfacet-wrap
You could use a custom function, you can use with the labeller argument, see here - RHA
It's not clear to me how you get the labeller argument of facet_grid to replace the factor with an expression and have the facets in rows with the labels on top, as in my example (rather than on the side as in facet_grid labels for rows). - user1701545
Did you check this topic ? It might help stackoverflow.com/questions/20037843/… - Boidot
It's close but my labels are compound - an italicized word followed by an non-italicized one. I don't see how I can achieve that with element_text of theme - user1701545

3 Answers

10
votes

As of ggplot2 2.1.0:

data(tips, package="reshape2")
library(ggplot2)
ggplot(tips, aes(x=total_bill, y=tip/total_bill)) + 
  geom_point(shape=1) + 
  facet_wrap(~sex, ncol=1, 
             labeller=label_bquote(.(levels(tips$sex)[sex])~subjects))
7
votes

Looks overly complicated, but works. You'll have to use facet_grid though.

make_label <- function(value) {
  x <- as.character(value)
  bquote(italic(.(x))~subjects)
}

plot_labeller <- function(variable, value) {
  do.call(expression, lapply(levels(value), make_label))
}

ggplot(tips, aes(x=total_bill, y=tip/total_bill)) + 
  geom_point(shape=1) + 
  facet_grid(.~sex, labeller = plot_labeller)

enter image description here

2
votes

The following works for R 4.0.3 and ggplot2 3.3.2

library(ggplot2)
data(tips, package="reshape2")
tips$sex = as.character(tips$sex)
sp <- ggplot(tips, aes(x=total_bill, y=tip/total_bill)) + 
  geom_point(shape=1) + 
  facet_wrap(~sex, ncol = 1, labeller = label_bquote(italic(.(sex))~subjects))
sp

It uses label_bquote as suggested by @Stéphane Laurent but does not require converting levels into the correct character within the bquote which failed for me.