Custom ggplot themes

I often want to consistently theme my ggplots across projects. I’ve developed some custom themes, but they’re usually ad-hoc, and don’t work particularly well in packages, because the simple way to do it isn’t a function.

library(ggplot2)

For example, we might have a theme that’s good for publication, as in Saving and theming plots, where we specify size, backgrounds, and text. We load new fonts first.

# Load local functions
devtools::load_all()

ℹ Loading galenR

showtext::showtext_auto()
pubfont <- 'Cambria'
loadfonts(fontvec = pubfont)

pubtheme <- theme_bw(base_size = 10) + 
  theme(strip.background = element_blank(),
        plot.background = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        text = element_text(family=pubfont))

Here, the theme is essentially hardcoded, and we can add it to a figure.

ggplot(iris, aes(x = Sepal.Length, y = Petal.Width, color = Species)) + 
  geom_point() + 
  facet_wrap(~Species) + 
  pubtheme

What’s the problem?

First, we have to adjust the theme with + if we want to make changes.

Most importantly, probably, is that in packages that gets read in as an object, instead of a function (which yes, are objects, but packages like functions).

Making it a function

The solution is to make it a function. This matches how the built-in themes work too, e.g. we add theme_bw(), not theme_bw , and that lets us modify it in the arguments. As a simple case, this lets us use the base_size to have a theme that we can give larger fonts to for talks vs papers, for example, whereas in the past I’d have two different names for that.

theme_pub <- function(base_size = 10) {
  ggplot2::theme_bw(base_size = base_size) +
    theme(strip.background = element_blank(),
        plot.background = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        text = element_text(family=pubfont))
}

This looks the same

ggplot(iris, aes(x = Sepal.Length, y = Petal.Width, color = Species)) + 
  geom_point() + 
  facet_wrap(~Species) +
  theme_pub()

Now, maybe we also want to make the font an argument? Now, we can include loadfonts to load it if it’s not already.

theme_pubf <- function(base_size = 10, font) {
  if (!(font %in% sysfonts::font_families())) {
      loadfonts(font)
  }

  ggplot2::theme_bw(base_size = base_size) +
    theme(strip.background = element_blank(),
        plot.background = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        text = element_text(family=font))
}

Now let’s change the font

ggplot(iris, aes(x = Sepal.Length, y = Petal.Width, color = Species)) + 
  geom_point() + 
  facet_wrap(~Species) +
  theme_pubf(base_size = 14, font = 'Calibri')

Can we pass other arguments?

If the goal is to enforce a style, we might not want to allow passing other arguments to theme, but can we with …?

theme_pub_dots <- function(base_size = 10, font, ...) {
  if (!(font %in% sysfonts::font_families())) {
      loadfonts(font)
  }

  ggplot2::theme_bw(base_size = base_size) +
    theme(strip.background = element_blank(),
        plot.background = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        text = element_text(family=font), 
        ...)
}

ggplot(iris, aes(x = Sepal.Length, y = Petal.Width, color = Species)) + 
  geom_point() + 
  facet_wrap(~Species) +
  theme_pub_dots(base_size = 8, font = 'Arial', legend.position = 'none')