I am super exciting to share with you my recent “discovery” of the {ggtext} R package.

I had looked for a solution to color individual words in the title of a {ggplot2} data visualization and {ggtext} provided me with a great solution for doing just that (and more).

So, how does it work? Have a look at this example:

library(ggplot2)
library(dplyr)
data(biomedicalrevenue, package = "ggcharts")

plot <- biomedicalrevenue %>%
  filter(company %in% c("Roche", "Novartis")) %>%
  ggplot(aes(year, revenue, color = company)) +
  geom_line(size = 1.2) +
  ggtitle(
    paste0(
      "**Roche**",
      " *overtook* **Novartis**",
      " in 2016"
    )
  ) +
  scale_color_manual(
    values = c("Roche" = "#93C1DE", "Novartis" = "darkorange"),
    guide = "none"
  ) +
  ggcharts::theme_hermit(ticks = "x", grid = "X")  +
  theme(plot.title = ggtext::element_markdown())
plot

Inside theme() I set plot.title = ggtext::element_markdown(). This has the effect that the plot title I created using ggtitle() is interpreted as markdown/HTML. That made it possible to have the title of the plot act as a legend by coloring the appropriate keywords.

To color words you have to wrap them inside a tag and use inline CSS to specify the color. In general with will look like this:

Text you want to color

Pay attention to the slash in the second tag. If you miss that it won’t render properly because that’s invalid HTML.

Notice also that inside of scale_color_manual() I set guide = "none". This results in no legend being drawn which would be redundant in this plot.

Quite a neat solution, isn’t it?

While you need to revert to HTML for coloring the text you can use markdown for making individual words bold (e.g. **Roche**), italics (e.g. *overtook*) and so forth. I love the flexibility this offers.

The {ggtext} package is not available from CRAN, yet, but you can install it from GitHub.

remotes::install_github("wilkelab/ggtext")

Setting individual theme elements to ggtext::element_markdown() can add quite a bit of boilerplate code to your plot. That’s why I decided to create the {mdthemes} package which provides themes that interpret text as markdown out of the box. Let’s contrast a “normal” theme with an md_theme. First, have a look at what happens if I add theme_minimal() to the plot I just created.

plot + theme_minimal()

As expected, the title is not rendered correctly because the plot.title theme element is overwritten. If you use md_theme_minimal(), however, it just works.

plot + mdthemes::md_theme_minimal()

Apart from the title, the subtitle, axis labels and captions are set to element_markdown() for all mdthemes.

plot +
  labs(
    x = "**Year**",
    y = "Revenue (*Billion* USD)",
    caption = "Data Source: *en.wikipedia.org/wiki/List_of_largest_biomedical_companies_by_revenue*"
  ) +
  mdthemes::md_theme_minimal()

The {mdthemes} packages currently contains all themes from {ggplot2}, {ggthemes}, {hrbrthemes}, {tvthemes} and {cowplot} with support for rendering text as markdown.

If you want to turn a theme that is not part of the {mdthemes} package into an md_theme you can use the as_md_theme() function.

plot + mdthemes::as_md_theme(theme_minimal())

Just like {ggtext}, the {mdthemes} package is currently only available from GitHub. You can install it by copy-pasting this code into your R console.

remotes::install_github("thomas-neitmann/mdthemes")