ggplot2: Font Style in label expression

Question

Changing font faces and sizes works well without expression in the labels. Here is the code where I've problem to change the font faces in label expression.

p <- ggplot(data = mtcars, aes(x=wt, y=mpg)) + 
    geom_point() + 
    labs(x="Weight", y=expression(paste("mpg (  ", m^{-2}, ")"))) + 
    theme(axis.title.x = element_text(family="serif", face="bold", 
        size=12, angle=00, hjust=0.54, vjust=0)) + 
    theme(axis.title.y = element_text(family="serif", face="bold", 
        size=12, angle=90, vjust=0.25))

p

Any help would be highly appreciated. Thanks

Answer 1

I do not think it is the presence of expression, although you don't say exactly what it is that you are seeing so it's difficult to be sure. On a Mac you get the xlab in bold-serif font, but the ylab is not bold (although it is in serif). If I use the plotmath bold it succeeds from inside the expression function:

p <- ggplot(data = mtcars, aes(x=wt, y=mpg)) + 
geom_point() + 
    labs(x = "Weight", y = expression(bold(mpg (m^-2) ))) +
    theme(axis.title.y = element_text(family="serif", 
        size = 12, angle = 90, vjust = 0.25)) +
    theme(axis.title.x = element_text(family="serif",
        size = 12, angle = 0, hjust = 0.54, vjust = 0))
p

As always, graphical devices are often OS-variable and you have not offered any hint about yours, so further commentary is inhibited.

(EDIT: If you quote the exponent -2 you can get it bold()-ed as well.)

expression( bold(mpg (m^bold("-2")) ) ) )