Dynamically formatting individual axis labels in ggplot2

Question

This may end up being an expression or call question, but I am trying to conditionally format individual axis labels.

In the following example, I'd like to selectively bold one of the axis labels:

library(ggplot2)

data <- data.frame(labs = c("Oranges", "Apples", "Cucumbers"), counts = c(5, 10, 12))

ggplot(data = data) + 
  geom_bar(aes(x = labs, y = counts), stat="identity")`

There is similar problem here, but the solution involves theme and element_text. I am trying to use axis labels directly.

I can do this manually as below:

breaks <- levels(data$labs)
labels <- breaks
labels[2] <- expression(bold("Cucumbers"))

ggplot(data = data) + 
  geom_bar(aes(x = labs, y = counts), stat="identity") + 
  scale_x_discrete(label = labels, breaks = breaks)

But, if I try to do it by indexing instead of typing out "Cucumbers", I get the following error:

breaks <- levels(data$labs)
labels <- breaks
labels[2] <- expression(bold(labels[2]))

ggplot(data = data) + 
  geom_bar(aes(x = labs, y = counts), stat="identity") + 
  scale_x_discrete(label = labels, breaks = breaks)

Which makes sense, because it is not evaluating the labels[2]. But, does anyone know how to force it to do that? Thanks.

Answer 1

How about

breaks <- levels(data$labs)
labels <- as.expression(breaks)
labels[[2]] <- bquote(bold(.(labels[[2]])))

ggplot(data = data) + 
  geom_bar(aes(x = labs, y = counts), stat="identity") + 
  scale_x_discrete(label = labels, breaks = breaks)

Here we are more explicit about the conversion to expression and we use bquote() to insert the value of the label into the expression itself.