Feature request: Is it possible to use legend.justification.* adjust the legend position directly in guide_colorbar

[Breeze-Hu]

Happy New Year in advance!

The update in version 3.5 https://www.tidyverse.org/blog/2024/02/ggplot2-3-5-0-legends/#placement mentions the fine adjustment of the legend position, which can now be done in combination with guides and theme.

It was the expected result and worked out well:

library(ggplot2)

ggplot(mpg, aes(displ, hwy, shape = factor(cyl), colour = cty)) +
  geom_point()+
  guides(color = guide_colorbar(position = 'bottom'))+
  theme(legend.justification.bottom = 'left')

Is it possible to do positional adjustments (top, bottom, left, right) in the guide in scale_*_* and guides in combination with the theme for the bottom-left position, etc.? Currently only adjusts to the bottom, but not to the right. legend.justification = 'left' or legend.justification.bottom = 'left' for both of the following does not work as expected:

ggplot(mpg, aes(displ, hwy, shape = factor(cyl), colour = cty)) +
  geom_point()+
  scale_color_continuous(
  guide =  guide_colorbar(position = 'bottom',
                        theme = theme(legend.justification.bottom = 'left')))

ggplot(mpg, aes(displ, hwy, shape = factor(cyl), colour = cty)) +
  geom_point()+
  guides(color = guide_colorbar(position = 'bottom',
                                theme =  theme(legend.justification.bottom = 'left')))

ggplot(mpg, aes(displ, hwy, shape = factor(cyl), colour = cty)) +
  geom_point()+
  scale_color_continuous(
    guide =  guide_colorbar(position = 'bottom',
                            theme = theme(legend.justification = 'left')))

ggplot(mpg, aes(displ, hwy, shape = factor(cyl), colour = cty)) +
  geom_point()+
  scale_color_continuous(
    guide =  guide_colorbar(position = 'bottom',
                            theme = theme(legend.justification = c(0,0))))

[teunbrand]

The justification of legends are a property of the legend boxes, not individual guides. We cannot let guides determine, in a bottom-up fashion, what the properties of legend boxes are because it would result in contorted code. At best, we can document more clearly which theme elements are ignored in guide_*(theme).

[Breeze-Hu]

I see. So isn't the difference roughly like the two boxes in the picture below?

[teunbrand]

That is roughly correct, except that the legend box is fit to the guides. You can visualise it using the theme(legend.box.background). Come to think of it, it probably wouldn't hurt to specify this in the documentation about legend.justification.

[Breeze-Hu]

At best, we can document more clearly which theme elements are ignored in guide_*(theme).

I'm in favor of this, users will have more clarity on what can be adjusted directly in guide_* and others need to go to the theme.