r - How to annotate() ggplot with latex

Question

I'd like to add latex text to a ggplot2 plot using annotate(). Using expression(), as described here for adding latex to axis labels, does not seem to work. To wit:

# Use expression() to create subscripted text
p <- ggplot(mpg, aes(x=cty, y=hwy)) + geom_point() +
  scale_x_continuous(expression(text[subscript])) 

# But expression() in annotate adds nothing to the plot
p + annotate("text", x=10, y=40, label=expression(text[subscript])) 

# Passing regular text to annotate works fine
p + annotate("text", x=10, y=40, label="foo") 

Why are expressions treated differently by annotate than by other ggplot functions? And how can I annotate with latex?

Answer 1

There is an R package called latex2exp which may be helpful. It has function TeX which accepts some LaTeX expressions enclosed with dollar sign $ as in this example:

library(latex2exp)
library(ggplot2)

qplot(1, "A")+
     ylab(TeX("Formula: $\frac{2hc^2}{\lambda^\beta}$"))+
     xlab(TeX("$\alpha$"))

More examples can be found in this vignette.