ggplot2 - having trouble with geom_text with facet_wrap

Question

I created a decent-looking figure in ggplot...

    pollinators_1 <- ggplot(data = pollinator_counts_hybrids, aes(x = pollinator.species, y = n, fill = taxa.visited)) +
      geom_bar(stat = 'identity') +
      facet_wrap(~ site, ncol = 1) +
      theme_classic() +
      labs(title = "Pollinators of Gentian taxa at sites with hybrids present", x = "Pollinator Species", y = "Number of Visits", fill = "Taxa")
    
    pollinators_2 <- pollinators_1 + scale_fill_manual('Taxa', values=c('#a1d99b', '#9ebcda', '#8856a755'))

pollinators_3 <- pollinators_2 + theme(axis.text.x = element_text(angle = 45, hjust = 1))

I would like to have some text in each facet_wrapped plot that is unique to that plot. I took this chunk of code:

dat_text <- data.frame(
  label = c("4 cylinders", "6 cylinders", "8 cylinders"),
  cyl   = c(4, 6, 8)
)
p + geom_text(
  data    = dat_text,
  mapping = aes(x = -Inf, y = -Inf, label = label),
  hjust   = -0.1,
  vjust   = -1
)

from a past StackOverflow question: Annotating text on individual facet in ggplot2 and made it to my own code:

text_pollinator_A <- data.frame(label = c("n = 11", "n = 15", "n = 10", "n = 10"),
                                site = c("BS", "LHF", "SHP", "SPN"))

pollinators_4 <- pollinators_3 + geom_text(data = text_pollinator_A, mapping = aes(x = -Inf, y = -Inf, label = label),
                                           hjust = -0.1,
                                           vjust = -1)

But I am receiving the error:

> pollinators_4
Error in `geom_text()`:
! Problem while computing aesthetics.
ℹ Error occurred in the 2nd layer.
Caused by error:
! object 'taxa.visited' not found
Run `rlang::last_trace()` to see where the error occurred.

If anyone could help me fix this, that would be great! Thank you!

Answer 1

You want the fill to only work on the bar, not the text. So remove aes(fill) from the global ggplot() call and move it to the geom_bar() layer. Here is the corrected code:

pollinators_1 <- ggplot(data = pollinator_counts_hybrids, 
                          aes(x = pollinator.species, y = n)) +
                 geom_bar(stat = 'identity',aes(fill=taxa.visited)) +
                 facet_wrap(~ site, ncol = 1) +
                 theme_classic() +
                 labs(title = "Pollinators of Gentian taxa at sites with hybrids present",
                          x = "Pollinator Species", y = "Number of Visits", 
                         fill = "Taxa")

pollinators_2 <- pollinators_1 + scale_fill_manual('Taxa', 
                                            values=c('#a1d99b', '#9ebcda', '#8856a755'))

pollinators_3 <- pollinators_2 + theme(axis.text.x = element_text(angle = 45, hjust = 1))

text_pollinator_A <- data.frame(label = c("n = 11", "n = 15", "n = 10", "n = 10"),
                                 site = c("BS", "LHF", "SHP", "SPN"))

pollinators_4 <- pollinators_3 + geom_text(data = text_pollinator_A, 
                                       mapping = aes(x = -Inf, y = -Inf, label = label),
                                       hjust = -0.1,
                                       vjust = -1)