Create a custom theme that can inherit theme parameters

February 9, 2022

I wish to create a custom theme function, which can inherit all the arguments from theme.

So far, I have something like:

my_theme <- function(...){
  theme(axis.title = element_text(colour = "red"))
}

If I want to change the plot background for example, I currently need to do:

ggplot(iris,
       aes(x = Species, y = Sepal.Length)) +
  geom_boxplot() +
  my_theme() +
  theme(panel.background = element_rect(fill = "blue",
                                        colour = "green"))

While I wish I could do:

ggplot(iris,
       aes(x = Species, y = Sepal.Length)) +
  geom_boxplot() +
  my_theme(panel.background = element_rect(fill = "blue",
                                        colour = "green"))

I guess I have to initialize all the theme’s arguments inside the custom function, but is there another work around? Thanks!

>Solution :

You could just pass on the ellipses to theme()?

library(ggplot2)

my_theme <- function(..., axis.title = NULL) {
  axis.title <- if (is.null(axis.title)) {
    element_text(colour = "red") 
  } else {
    axis.title
  } 
  theme(axis.title = axis.title, ...)
}

# Alternatively
my_theme <- function(..., axis.title = element_text(colour = "red")) {
  theme(axis.title = axis.title, ...)
}

ggplot(iris,
       aes(x = Species, y = Sepal.Length)) +
  geom_boxplot() +
  my_theme(panel.background = element_rect(fill = "blue",
                                           colour = "green"))

^{Created on 2022-02-09 by the reprex package (v2.0.1)}

Another option if you’re writing scripts/notebooks for yourself with no intention to package up your code is to just use theme_set() at the beginning, which propagates to all subsequent plots. This is how most of my scripts start.

library(ggplot2)

theme_set(theme_get() + theme(axis.title = element_text(colour = "red")))

ggplot(iris,
       aes(x = Species, y = Sepal.Length)) +
  geom_boxplot() +
  theme(panel.background = element_rect(fill = "blue",
                                        colour = "green"))