Change geom_text to bold when parse=TRUE

Question

I am annotating faceted plots to include a superscript, yet am having trouble making the text bold. I realise that this has something to do with creating an expression outside the plot call and then specifying parse=TRUE. There is probably quite a simple solution but so far nothing I have tried has worked, including the use of bquote() and bold(). Thanks

library(ggplot2)

data(iris)

rsq<-c(.3,.6,.75)
pos<-c(5,6,7)
Species<-levels(iris$Species)

big_data<-as.data.frame(cbind(pos, rsq))
big_data$Species<-Species

lab <- paste("r^2 == ", round(big_data$rsq,2))

ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width)) +
  facet_wrap(~Species,scales='free_x')+
  geom_point(size=3,show.legend = F) +
  geom_text(aes(x=pos,y=1,label=as.character(lab)),parse=TRUE,data=big_data,fontface='bold')

Answer 1

you can get r to be bold()

lab <- sprintf("bold(r)^2 == %.2f", big_data$rsq)

but that's about it. From ?plotmath

Note that bold, italic and bolditalic do not apply to symbols, and hence not to the Greek symbols such as mu which are displayed in the symbol font. They also do not apply to numeric constants.

Your best bet for finer typography might be tikzDevice.

Answer 2

I know this is big time excavating, but for those who stumble upon this post like me, you can use ggtext to get the formatting you like:

library(ggplot2)
library(ggtext)
big_data <- data.frame(
    pos = 5:7, 
    Species = levels(iris$Species),
    lab = paste0("<b>r<sup>2</sup> = ", sprintf("%.2f", c(.3,.6,.75), 2), "</b>")) 
ggplot(iris, aes(x=Sepal.Length, y = Sepal.Width)) +
    facet_wrap(~Species, scales='free_x')+
    geom_point(size = 3, show.legend = FALSE) +
    geom_richtext(data = big_data, aes(x = pos, y = 1, label = lab),
        fill = NA, label.color = NA,
        label.padding = grid::unit(rep(0, 4), "pt")
    )

^{Created on 2021-01-25 by the reprex package (v0.3.0)}

Answer 3

A little cheat - over plotting the text 3 times with slight increases in size.

ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width)) +
  facet_wrap(~Species,scales='free_x')+
  geom_point(size=3,show.legend = F) +
  geom_text(aes(x=pos,y=1,label=as.character(lab)),parse=TRUE,data=big_data,size=4)+
  geom_text(aes(x=pos,y=1,label=as.character(lab)),parse=TRUE,data=big_data,size=4.07)+
  geom_text(aes(x=pos,y=1,label=as.character(lab)),parse=TRUE,data=big_data,size=4.08)