Customize small multiple appearance with ggplot2

This page aims to provide useful R code to customize the strips of a ggplot2 plots when using faceting. For other ggplot2 customization, visit the dedicated page.

Here we want to modify non-data components, which is often done trough the theme() command. This page is strongly inspired from the help page of ggplot2 (?theme). Also, do not hesitate to visit the very strong ggplot2 documentation for more information.

Chart 1 is a really basic plot relying on the mtcars dataset. The 3 following charts show how to customize strip background, text, and how to modify the space between sections.

library(ggplot2)
 
# basic chart
basic=ggplot(mtcars, aes(wt, mpg)) +
    geom_point() +
    facet_wrap(~ cyl)
basic

# Change background
basic + theme(strip.background = element_rect(colour = "red", fill = alpha("blue",0.2) ))

# Change the text 
basic + theme(strip.text.x = element_text(colour = "red", face = "bold", size=10, angle=30))

# Change the space between parts:
basic + theme(panel.spacing = unit(4, "lines"))