ggplot: Using strip.text.x (element_text) for making only one element of the facet axis label "bold"

Question

I want to use bold face only on the first element of my top x axis label (in the facet panel). This can be done using the element_text function. However, when I do the following, all elements in the facet are turned to "bold", while I only want the first one to be bold.

p3 <- ggplot(mtcars, aes(wt, mpg)) + geom_point() + facet_wrap(~ cyl)
p3 + theme(strip.text.x = 
           element_text(colour = "white", face = c("bold", "plain", "plain")))

Therefore, in here, I only want the label "4" at the top to be bold.

Using Grob

p3 <- ggplot(mtcars, aes(wt, mpg)) + geom_point() + facet_wrap(~ cyl)
p3 <- p3 + theme(strip.text.x = 
           element_text(colour = "white", face = c("bold", "plain", "plain")))
grob <- ggplotGrob(p3)
elem <- grob$grobs$strip_t.1
elem

NULL

grid.ls(getGrob(elem, "strip.text.x.text", grep=TRUE))$name

Error in getGrob(elem, "strip.text.x.text", grep = TRUE) : it is only valid to get a child from a "gTree"

have you checked here - https://stackoverflow.com/questions/9847559/conditionally-change-panel-background-with-facet-grid — Hardik Gupta, Oct 24 '17 at 08:54
And this as well - https://stackoverflow.com/questions/6750664/how-to-change-the-format-of-an-individual-facet-wrap-panel — Hardik Gupta, Oct 24 '17 at 09:00
@Hardikgupta labels are more difficult, I don't think that your suggestions would work here — pogibas, Oct 24 '17 at 09:02
@PoGibas, actually the accepted answer in the second link of Hardik shows grob manipulation, including changing the strip text. — Axeman, Oct 24 '17 at 09:07
@Axeman thanks! This is what I get for rushing and being too cocky — pogibas, Oct 24 '17 at 09:14

Marco Sandri · Accepted Answer · 2017-10-24T13:19:23.583

library(ggplot2)
library(grid)
p3 <- ggplot(mtcars, aes(wt, mpg)) + geom_point() + facet_wrap(~ cyl) +
                 theme(strip.text.x = element_text(colour = "white"))
grob <- ggplotGrob(p3)
print(grob) 
# ...
# 17  2 ( 6- 6, 4- 4) strip-t-1-1                                   gtable[strip]
# 18  2 ( 6- 6, 8- 8) strip-t-2-1                                   gtable[strip]
# 19  2 ( 6- 6,12-12) strip-t-3-1                                   gtable[strip]
# ...

# The first strip grob is at position 17
k <- 17
# Here I increase font size for a better visualization of the bold font
grob$grobs[[k]]$grobs[[1]]$children[[2]]$children[[1]]$gp$fontsize <- 20
# Set again white color for strip text
grob$grobs[[k]]$grobs[[1]]$children[[2]]$children[[1]]$gp$col <- "white"
# Set bold font
grob$grobs[[k]]$grobs[[1]]$children[[2]]$children[[1]]$gp$font <- as.integer(2)
attr(grob$grobs[[k]]$grobs[[1]]$children[[2]]$children[[1]]$gp$font,"names") <- "bold"

grid.draw(grob)

Unfortunately, I can see that all of the labels are bold. You have all of the labels (`4`, `6`, and `8`) made bold. But as I mentioned I only want `4` to stay bold. Everything else (`6` and `8`) should stay plain! — dulafil, Oct 24 '17 at 13:05
This is really great. It is amazing how many 'hidden' alleys ggplot has! Thank you for your help. — dulafil, Oct 24 '17 at 13:59

ggplot: Using strip.text.x (element_text) for making only one element of the facet axis label "bold"

1 Answers1