Legend size adjustment within guides

[Breeze-Hu]

Hi!

When I tried to adjust the legend.key.size in guides it doesn't seem to work as expected. But legend.key.spacing.y works fine.
When I include it in the theme(adjusting the whole legend?) , the code works very well.

I'm not sure if this is similar to the question below? Or is it a bug? If this behavior is indeed due to an underlying mechanism, wouldn’t it be preferable for the documentation to include a note about it, as is done for this issue?
#6263

Here is the code to reproduce the issue:

library(tidyverse)

data = tibble(x = rep(c('a','b'),each = 10),
              y = runif(20,min = 0, max=10))

ggplot(data = data, aes(x = x, y = y, fill = x))+
  geom_boxplot()+
  guides(fill = guide_legend(theme = theme(legend.key.spacing.y = unit(5,'lines'),
                                           legend.key.size = unit(3, 'lines')))
         )

ggplot(data = data, aes(x = x, y = y, fill = x))+
  geom_boxplot()+
  guides(fill = guide_legend(theme = theme(legend.key.spacing.y = unit(5,'lines')))
  )+
  theme(legend.key.size = unit(3, 'lines'))

[teunbrand]

Thanks for the report! This is because the legend.key.width/legend.key.height are precomputed from the main theme, so setting the parent legend.key.size locally is ineffective. I'm not 100% convinced this is an actual bug, but I can see why this is confusing and we should consider changing this.

[teunbrand]

A more minimal reprex:

library(ggplot2)
big_keys <- theme(legend.key.size = unit(3, "cm"))

p <- ggplot(mpg, aes(displ, hwy, colour = drv)) +
  geom_point()

p + big_keys

p + guides(colour = guide_legend(theme = big_keys))

^{Created on 2025-02-19 with reprex v2.1.1}

[Breeze-Hu]

This is because the legend.key.width/legend.key.height are precomputed from the main theme, so setting the parent legend.key.size locally is ineffective.

Get!

I'm not 100% convinced this is an actual bug

I totally agree with this statement.

Looking forward to the follow up. Thank you!!!