Italic letters in generated axis tick labels-CodePudding

I have an issue creating axis tick labels that combine italic letters and input of variables. Simply said, I want to call variables and insert text such as n = 1 below each label.

Here's an example with everything but the italic n:

require(ggplot2)

mpg$class <- as.factor(mpg$class)
counts <- rep(1:7, 1)

ggplot(mpg, aes(class, hwy))  
  geom_boxplot()  
  scale_x_discrete(labels = paste(levels(mpg$class), "\nn = ", counts, sep = ""))

My first thought was to use the Unicode for an italic N, like I've done for superscript numbers in the past. But for some reason, the letter is too small & stylistically mismatched with the rest of the text. More importantly, in my real use-case, all Unicode characters for italic n appear to render out of alignment, depressed somewhere halfway between normal and subscript.

ggplot(mpg, aes(class, hwy))  
  geom_boxplot()  
  scale_x_discrete(labels = paste(levels(mpg$class), "\n\U1D45B = ", counts, sep = ""))

So, I found the plotmath function ~italic(x) could be used to italicize letters. However, there's a clear and unexpected failure when I incorporate it in the paste() line for the x-axis tick labels. Note that the function does work in xlab()

ggplot(mpg, aes(class, hwy))  
  geom_boxplot()   xlab(~italic("n"))  
  scale_x_discrete(labels = paste(levels(mpg$class), "\n", ~italic("n"), " = ", counts, sep = ""))

I have searched StackOverflow for similar cases. However, none of them need to call for variables:

Add greek letters to axis tick labels in R

Changing one character in axis tick labels to italic while keeping multiple lines

How to change into italic style one letter in R plot without adding a space

How to italicize part (one or two words) of an axis title

I have tried understanding how to use expression() and bquote() while being able to call variables, but I have been unable to produce anything functional.

At this point, any help is very appreciated!

CodePudding user response：

These days, you can use the ggtext package to style your text with some markdown/html decorations.

library(ggplot2)
library(ggtext)
#> Warning: package 'ggtext' was built under R version 4.1.1

mpg$class <- as.factor(mpg$class)
counts <- rep(1:7, 1)

ggplot(mpg, aes(class, hwy))  
  geom_boxplot()  
  scale_x_discrete(
    labels = paste0(levels(mpg$class), "<br><i>n = ", counts, "</i>")
  )  
  theme(axis.text.x = element_markdown())

^{Created on 2021-10-16 by the reprex package (v2.0.0)}