`legend.key.size`/`legend.key.width`/`legend.key.height` bug

[kylebutts]

Sorry for the very long reprex, but I tried to make it complete (and easy to debug)

1. When right/left legend, the legend.key.height does not work
2. When top/bottom legend, the legend.key.width does not work

library(ggplot2)
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.title.position = "top",
    legend.key.width = unit(12, "pt"),
    legend.key.height = unit(12, "pt")
  )

# Height does not work
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.title.position = "top",
    legend.key.width = unit(12, "pt"),
    legend.key.height = unit(48, "pt")
  )

# Width works
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.title.position = "top",
    legend.key.width = unit(48, "pt"),
    legend.key.height = unit(12, "pt")
  )

# size changes height
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.title.position = "top",
    legend.key.size = unit(48, "pt"),
    legend.key.width = unit(12, "pt"),
  )

# can override with width
# can not override with height
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.title.position = "top",
    legend.key.size = unit(48, "pt"),
    legend.key.width = unit(12, "pt"),
    legend.key.height = unit(12, "pt")
  )

# when using `legend.position = "bottom"`, width now causes the problems
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.position = "bottom",
    legend.title.position = "top",
    legend.key.width = unit(12, "pt"),
    legend.key.height = unit(12, "pt")
  )

# Height works
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.position = "bottom",
    legend.title.position = "top",
    legend.key.width = unit(12, "pt"),
    legend.key.height = unit(48, "pt")
  )

# Width does not work
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.position = "bottom",
    legend.title.position = "top",
    legend.key.width = unit(48, "pt"),
    legend.key.height = unit(12, "pt")
  )

# size changes width
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.position = "bottom",
    legend.title.position = "top",
    legend.key.size = unit(48, "pt"),
    legend.key.height = unit(12, "pt"),
  )

# can override with height
# can not override with width
ggplot() +
  geom_point(aes(x = mpg, y = hp, color = hp), mtcars) +
  theme(
    legend.position = "bottom",
    legend.title.position = "top",
    legend.key.size = unit(48, "pt"),
    legend.key.width = unit(12, "pt"),
    legend.key.height = unit(12, "pt")
  )

^{Created on 2025-04-16 with reprex v2.1.1}

[teunbrand]

This is because the default for guide_legend() is to have a 1:1 width:height ratio and guide_colourbar() has a default of 1:5 for vertical direction and 5:1 for horizontal direction. We cannot encode these three scenarios in a single theme, so these guides have so called 'local defaults', where colourbars use rel(5) for their width/height depending on orientation. In that case, it will just inherit 5 * legend.key.size for width/height instead of direct inheritance.

The local theme can be set in the guide itself, so you can do the following:

  scale_colour_continuous(
    guide = guide_colourbar(theme = theme(
      legend.key.height = unit(12, "pt"),
      legend.key.width  = unit(36, "pt")
    ))
  )

to have literal values for the colourbar. I'd argue what you are seeing is intended behaviour and not a bug.

[kylebutts]

@teunbrand thanks for the information; that clarifies things. In the past, specifying width and height in the theme call works; hence the confusion.