Different alignment of legend labels when removing the legend title

[Eluvias]

# v3.0.0
library(ggplot2)
#> Warning: package 'ggplot2' was built under R version 3.5.1

p <- ggplot(mpg, aes(class, fill = class)) + 
     geom_bar()

p

# different alignment of legend labels
p + theme(legend.title = element_blank())

Created on 2018-07-07 by the reprex package (v0.2.0).

[clauswilke]

What is happening is that the size of the spacing is calculated from the font size of the legend title, and where there is none the font size is set to zero. These are the relevant lines of code:

ggplot2/R/guide-legend.r

Lines 330 to 336 in 3d022ed

	title_fontsize <- title.theme$size %||% calc_element("legend.title", theme)$size %||% 0
	# gap between keys etc
	# the default horizontal and vertical gap need to be the same to avoid strange
	# effects for certain guide layouts
	hgap <- width_cm(theme$legend.spacing.x %||% (0.5 * unit(title_fontsize, "pt")))
	vgap <- height_cm(theme$legend.spacing.y %||% (0.5 * unit(title_fontsize, "pt")))

Arguably, it would make sense to try the general font size from the generic text theme element. However, as the code shows, you can work around this issue by setting legend.spacing.x and legend.spacing.y. By default they are set to half the font size.

library(ggplot2)

ggplot(mpg, aes(class, fill = class)) + 
  geom_bar() + 
  theme(
    legend.title = element_blank(),
    legend.spacing.x = unit(11/2, "pt") # default font size is 11pt
  )

Created on 2018-07-07 by the reprex package (v0.2.0).

[ptoche]

Another workaround (trivial remark here): If you do not need to go through a theme(), you can reset the title with the guides, something like p + guides(fill = guide_legend(title = "")) or p + guides(fill = guide_legend(title = NULL)).

[clauswilke]

@ptoche I'd always recommend setting titles to NULL rather than to "" since the former completely eliminates the title whereas the latter reserves space and just doesn't print anything there.

Exaggerated example:

library(ggplot2)

ggplot(mpg, aes(class, fill = class)) + 
  geom_bar() + 
  scale_fill_discrete(name = NULL) +
  theme(legend.title = element_text(size = 500),
        legend.spacing.x = unit(5.5, "pt"),
        legend.spacing.y = unit(5.5, "pt"))

ggplot(mpg, aes(class, fill = class)) + 
  geom_bar() + 
  scale_fill_discrete(name = "") +
  theme(legend.title = element_text(size = 500),
        legend.spacing.x = unit(5.5, "pt"),
        legend.spacing.y = unit(5.5, "pt"))

Created on 2018-07-07 by the reprex package (v0.2.0).

[paleolimbot]

It's worth noting that #3180 is also about the vertical spacing of items in guide_legend()

[clauswilke]

This was fixed for 3.2.0. Apologies for not closing the issue.

library(ggplot2)

ggplot(mpg, aes(class, fill = class)) + 
  geom_bar() +
  theme(legend.title = element_blank())

^{Created on 2019-06-17 by the reprex package (v0.3.0)}

Session info

devtools::session_info()
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#>  date     2019-06-17                  
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[lock]

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