Home How to pass an anonymous function to labeller argument in ggplot's facet_wrap() to add text to the existing labels?

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How to pass an anonymous function to labeller argument in ggplot's facet_wrap() to add text to the existing labels?

byMR

May 5, 2024

How can I paste an additional constant text to ggplot facet labels?

For example, I have this current plot:

library(ggplot2)

df <- data.frame(
  x = rnorm(120, c(0, 2, 4)),
  y = rnorm(120, c(1, 2, 1)),
  z = letters[1:3]
)

ggplot(df, aes(x, y)) + 
  geom_point() + 
  facet_wrap(~z)

^{Created on 2024-05-05 with reprex v2.0.2}

Now let’s say that I want to add the same prefix (Foo = ) string to all facet labels:

If I do

ggplot(df, aes(x, y)) + 
  geom_point() + 
  facet_wrap(~z, labeller = \(x) paste("foo = ", x))

I get:

How can I tweak the function I pass to labeller to show foo = [preexisting label] ?

>Solution :

You have to wrap your function inside labeller() like so:

library(ggplot2)

set.seed(123)

df <- data.frame(
  x = rnorm(120, c(0, 2, 4)),
  y = rnorm(120, c(1, 2, 1)),
  z = letters[1:3]
)

ggplot(df, aes(x, y)) +
  geom_point() +
  facet_wrap(~z,
    labeller = labeller(z = \(x) paste("foo = ", x))
  )