ggplot2: Font Style in label expression

Solution 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")) ) ) )