Bold the first line of strings that are assigned to y-axis text in ggplot2 in r

Question

Considering the followinf dataframes as an example

DF1 <- data.frame(A = c(1, 2, 3), B = c("a", "b", "c"))
DF2 <- data.frame(Y = paste0("this is the first line thats bold ", DF1$A, "\n",
                            "this is the second line thats plain ", DF1$B),
                 X = structure(c(18903, 18965, 19081), class = "Date"))

DF2 looks like this:

> DF2
                                                                           Y          X
1 this is the first line thats bold 1\nthis is the second line thats plain a 2021-10-03
2 this is the first line thats bold 2\nthis is the second line thats plain b 2021-12-04
3 this is the first line thats bold 3\nthis is the second line thats plain c 2022-03-30

Now if I create a simple scatter plot of this data:

ggplot(DF2, aes(x = X, y = Y)) + geom_point()

How can I make the first line of the y-axis text bold? so I want the this is the first line thats bold 1(2,3) be bold and the this is the second line thats plain A(B,C) to remain plain.

Answer 1

ggtext package allows to format axis text as Markdown:

library(ggtext)
library(tidyverse)

DF1 <- data.frame(A = c(1, 2, 3), B = c("a", "b", "c"))
DF2 <- data.frame(
  Y = paste0(
    "this is the first line thats bold ", DF1$A, "\n",
    "this is the second line thats plain ", DF1$B
  ),
  X = structure(c(18903, 18965, 19081), class = "Date")
)


DF2 %>%
  mutate(Y = Y %>% str_replace("^", "**") %>% str_replace("\n", "**\n\n")) %>%
  ggplot(aes(x = X, y = Y)) +
  geom_point() +
  theme(axis.text.y = element_markdown())

^{Created on 2022-04-27 by the reprex package (v2.0.0)}