Show letters as key glyphs for geom_text legend instead of default 'a'

Question

I'm using geom_raster and geom_text to put a letter on each of the coloured rectangles in my plot. I'd like this letter to appear on top of the color boxes in the legend as well, but cannot figure out how.

I've tried adding show.legend=TRUE to the geom_text, but this results in the letter 'a' in each legend key, instead of the desired character.

The desired result looks as follows:

Here is code to reproduce the basic plot:

library(tidyverse)
d <-tribble(
    ~a, ~b, ~c,
    "a", "l", "A",
    "a", "r", "F",
    "b", "l", "Q",
    "b", "r", "R"
)

ggplot(data=d, aes(x=a, y=b, fill=c)) +
    geom_raster(na.rm=TRUE) +
    geom_text(aes(label=c), size=3, na.rm=TRUE) 

And the output:

This might be related to this issue: https://github.com/tidyverse/ggplot2/issues/2004, but perhaps there's a workaround?

Answer 1

You can use geom_point instead and specify point shape as letters with scale_shape_manual(values = d$c).

# We have to remove legend text and label with theme
ggplot(d, aes(a, b, fill = c, shape = c)) +
    geom_raster() +
    geom_point(size = 3) +
    scale_shape_manual(values = d$c) +
    theme(legend.text = element_text(size = 0),
          legend.title = element_text(size = 0))