r ggplot2: varying font sizes in legend

Question

I have two lines in my legend. How can I make one line bold, colour blue and large font and one line with small fonts, colour red and in italics?

library(ggplot2)
library(gridExtra)
p <- qplot(data = mtcars, wt, mpg)
print(arrangeGrob(p, legend = 
  textGrob("large font size colour blue bold\n small font size colour red italic", 
           rot = -90, vjust = 1)))

Thank you for your help.

Answer 1

You need to split your text into two textGrobs:

library(ggplot2)
library(gridExtra)
p <- qplot(data = mtcars, wt, mpg)
t1 <- textGrob("small font size colour red italic",
               gp = gpar(fontsize = 12, col = 'red', fontface = 'italic'), 
               rot = -90, vjust = 1)
t2 <- textGrob("large font size colour blue bold", 
               gp = gpar(fontsize = 20, col = 'blue', fontface = 'bold'), 
               rot = -90, vjust = 1)
print(arrangeGrob(p, t1, t2, widths = c(9/10, 1/20, 1/20), nrow = 1))

Answer 2

A solution using expression and atop:

p <- qplot(data = mtcars, wt, mpg)
print(arrangeGrob(p, legend=
      textGrob(expression(atop("large font size colour blue bold\n", atop(italic("small font size colour red italic")))),
      rot = -90, vjust = 1, gp=gpar(fontsize=16,fontface="bold"))))