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))

Solution

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)

Comments

[Jota]

Is adding fontface = "italic" not an option: ggplot(data = df, aes(x = V1, y = V2)) + geom_point() + geom_text_repel(aes(label = V3), fontface = "italic") ?

[hrbrmstr]

To be somewhat fair to the OP, the help on those _repel functions fail to include all supported aesthetics directly in the text but it does say "See the documentation for those functions [geom_text/geom_label] for more details"

[Bob]

Sorry, in a rush, I forgot to include that only a substring of the label is to be italicized; I will amend the question.

[alistaire]

If you use parse = TRUE you can use ?plotmath, though you'll have to reconfigure your labels.

[Bob]

Thank you! As an aside, this actually appears not to work in the current stable version of ggrepel, but the development version supports plotmath expressions. (github.com/slowkow/ggrepel/issues/60). If you would like, you can post as an answer so I can mark your answer as correct.

[mindlessgreen]

element_text() has an argument called face. I am not sure why geom_text() doesn't have this option.

[Megatron]

FYI, to see possible rendering options: demo(plotmath)

[hd1]

geom_text() calls the option fontface -- cookbook-r.com/Graphs/Fonts

[alistaire]

@hd1 From the question: "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."