geom_text() place text in a corner

Question

To reproduce:

library(tidyverse)

# use this for geom_text annotation
diamonds_annotations <- diamonds |> 
  group_by(cut) |> 
  summarise(SD_Price = paste0("sd = ", round(sd(price)), 2),
            Cor_Price = paste0("cor = ", round(cor(price, carat), 2)))


diamonds |> 
  ggplot(aes(x = carat, y = price)) +
  geom_point() +
  facet_wrap(. ~ cut)

This gives me a plot:

I would like to annotate the facets with the standard deviation sd() of price and also with the correlation cor() of price with carat. Tried:

diamonds |> 
  ggplot(aes(x = carat, y = price)) +
  geom_point() +
  facet_wrap(. ~ cut) +
  geom_text(data = diamonds_annotations, mapping = aes(x = -Inf, y = -Inf, label = SD_Price)) +
  geom_text(data = diamonds_annotations, mapping = aes(x = -Inf, y = -Inf, label = Cor_Price))

Here it looks like the text is cut off along the bottom. Tried several variations of playing with vjust and hjust e.g:

diamonds |> 
  ggplot(aes(x = carat, y = price)) +
  geom_point() +
  facet_wrap(. ~ cut) +
  geom_text(data = diamonds_annotations, mapping = aes(x = -Inf, y = -Inf, label = SD_Price), vjust = -8, hjust = -3, size = 3) +
  geom_text(data = diamonds_annotations, mapping = aes(x = -Inf, y = -Inf, label = Cor_Price), vjust = -6, hjust = -2, size = 3)

Here I can see the text cut off but still 'there' over on the right hand side.

This feels too fiddly and I wondered if I was doing something 'wrong'. Is there a way to consistently position the text in a corner, e.g. in this plot the bottom right hand side tends to be open space... is there a way to align right and bottom?

Same question e.g. right and top?

there might be something to do this in the `cowplot` package ... ? — Ben Bolker, Mar 01 '22 at 22:08
@BenBolker it's possible purely within ggplot and without grob-hacking now that we can extract ranges from a plot object easily (see below) — Allan Cameron, Mar 01 '22 at 22:27

score 3 · Accepted Answer · answered Mar 01 '22 at 22:24

This is tricky, but possible. First, create the plot without annotations:

p <- diamonds |> 
  ggplot(aes(x = carat, y = price)) +
  geom_point() +
  facet_wrap(. ~ cut)

Now get the x and y ranges from the plot object:

x_range <- layer_scales(p)$x$range$range
y_range <- layer_scales(p)$y$range$range

Now we can use this information to add text at a fixed position within each facet:

p + geom_text(data = diamonds_annotations,
              x = x_range[2] - 0.1 * (diff(x_range)),
              y = y_range[1] + 0.1 * (diff(y_range)),
          aes(label = paste(SD_Price, Cor_Price, sep = "\n")),
          hjust = 1)

Similarly, for a fixed position in the top right, we can do:

p + geom_text(data = diamonds_annotations,
              x = x_range[2] - 0.1 * (diff(x_range)),
              y = y_range[2] - 0.1 * (diff(y_range)),
          aes(label = paste(SD_Price, Cor_Price, sep = "\n")),
          hjust = 1)

I've played around a bit with such things before @DougFir - e.g. https://stackoverflow.com/questions/63741925/use-npc-units-in-annotate — Allan Cameron, Mar 01 '22 at 22:30
Also see ggpp package's geom_text_npc() as this is the easiest way to deal with varying y / x scales across each facet. — mkrasmus, Dec 22 '22 at 11:58

geom_text() place text in a corner

1 Answers1