r - How do I include italic text in geom_text_repel or geom_text labels for ggplot?

Question

Is it possible to pass partially italicized text labels into ggplot? I have tried using the expression and italic commands (expression(paste(italic("some text")))), but these cannot be passed into a data frame because the result of the commands is not atomic. Setting the parameter fontface = "italic" also doesn't suffice, since this italicizes the entire label, rather than just a select set of characters in the label. For instance, I would like some necessarily italicized Latin phrases to be italicized in a label (such as "in vivo" in "in vivo point").

library(ggplot)
library(ggrepel)

df <- data.frame(V1 = c(1,2), V2 = c(2,4), V3 = c("in vivo point","another point"))

ggplot(data = df, aes(x = V1, y = V2)) + geom_point() + geom_text_repel(aes(label = V3))

Answer 1

You can use parse = TRUE to pass ?plotmath expressions (as strings) to geom_text or geom_text_repel. You'll have to rewrite the strings as plotmath, but if it's not too many it's not too bad.

df <- data.frame(V1 = c(1,2), V2 = c(2,4), 
                 V3 = c("italic('in vivo')~point", "another~point"))

ggplot(data = df, aes(x = V1, y = V2, label = V3)) + 
    geom_point() + 
    geom_text_repel(parse = TRUE)