Cannot conditionally make axis labels bold in ggplot

Question

I am trying to make select axis labels bold, based on a conditional from a different column. In the code below, if Signif equals 1, then the Predictor axis text should be bold. In addition, the segments should appear in the order of Values increasing value.

However, this code is not changing any of the the axis texts to bold.

library(tidyverse)
library(ggtext)
library(glue)

df <- tibble(Predictor = c("Blue","Red","Green","Yellow"),
             Value = c(1,3,2,4),
             Signif = c(0,1,0,1))

df <- df %>% mutate(Predictor = ifelse(Signif==1,
                                 glue("<span style = 'font-weight:bold'>{Predictor}</span>"),
                                 glue("<span style = 'font-weight:plain'>{Predictor}</span>"))
)

df %>% 
  arrange(desc(Value)) %>% 
  mutate(Predictor=factor(Predictor, 
                          levels=df$Predictor[order(df$Value)])) %>%
  ggplot(aes(x=Predictor, y=Value)) +
  geom_segment(aes(xend=Predictor, yend=0)) +
  theme(axis.text.x = element_markdown())

If instead I use element_text() in the last line, and skip the mutate to markdown step above:

df %>% 
  arrange(desc(Value)) %>% 
  mutate(Predictor=factor(Predictor, 
                          levels=df$Predictor[order(df$Value)])) %>%
  ggplot(aes(x=Predictor, y=Value)) +
  geom_segment(aes(xend=Predictor, yend=0)) +
  theme(axis.text.x = element_text(face = if_else(df$Signif==1, "bold", "plain"))) 

It bolds the 2nd and 4th axis label, which corresponds to the Signif equals 1 in the original df.

How can I get the correct axis text labels to appear in bold?

Answer 1

I would’ve expected your code to work honestly, but you can use <b> instead of <span style...>:

library(tidyverse)
library(ggtext)
library(glue)

df <- df %>% 
  mutate(Predictor = ifelse(Signif==1,
                            glue("<b>{Predictor}</b>"),
                            Predictor))

df %>% 
  arrange(desc(Value)) %>% 
  mutate(Predictor=factor(Predictor, 
                          levels=df$Predictor[order(df$Value)])) %>%
  ggplot(aes(x=Predictor, y=Value)) +
  geom_segment(aes(xend=Predictor, yend=0)) +
  theme(axis.text.x = element_markdown())