How can I manipulate the strip text of facet_grid plots?

Question

I'm wondering how I can manipulate the size of strip text in facetted plots. My question is similar to a question on plot titles, but I'm specifically concerned with manipulating not the plot title but the text that appears in facet titles (strip_h).

As an example, consider the mpg dataset.

    library(ggplot2)      qplot(hwy, cty, data = mpg) + facet_grid( . ~ manufacturer) 

The resulting output produces some facet titles that don't fit in the strip.

I'm thinking there must be a way to use grid to deal with the strip text. But I'm still a novice and wasn't sure from the grid appendix in Hadley's book how, precisely, to do it. Also, I was afraid if I did it wrong it would break my washing machine, since I believe all technology is connected through The Force :-(

Many thanks in advance.

Answer 1

You can modify strip.text.x (or strip.text.y) using theme_text(), for instance

qplot(hwy, cty, data = mpg) +        facet_grid(. ~ manufacturer) +        opts(strip.text.x = theme_text(size = 8, colour = "red", angle = 90)) 

Update: for ggplot2 version > 0.9.1

qplot(hwy, cty, data = mpg) +        facet_grid(. ~ manufacturer) +        theme(strip.text.x = element_text(size = 8, colour = "red", angle = 90)) 

Answer 2

Nowadays the usage of opts and theme_text seems to be deprecated. R suggests to use theme and element_text. A solution to the answer can be found here: http://wiki.stdout.org/rcookbook/Graphs/Facets%20%28ggplot2%29/#modifying-facet-label-text

qplot(hwy, cty, data = mpg) +        facet_grid(. ~ manufacturer) +        theme(strip.text.x = element_text(size = 8, colour = "red", angle = 90))