Justifying the legend with respect to the full plot area rather than the panel

[LiRogers]

Now that the plot titles and captions can be aligned with respect to the full plot area, it would be great if the same was true for the legend. At the moment, if the legend is positioned at the top of the plot below the title it is aligned to the plot panel, making it misaligned with the title:

library(ggplot2)

ggplot(data = diamonds, mapping = aes(x = carat, y = price, color = cut)) +
  geom_point() +
  labs(title = "A plot title") +
  theme(plot.title.position = "plot",
        legend.position = "top",
        legend.justification = "left")

^{Created on 2020-05-22 by the reprex package (v0.3.0)}

Experimenting with negative values in legend.justification = c(x,y) can get the legend to align with the title, but the value is dependent on the size of the y-axis labels

[clauswilke]

Yes, that's a good point. Marking this as TODO for ggplot2 3.4.

[teunbrand]

Possibly related, #3989 also proposes more legend alignment options

[thomasp85]

Agreed that this would make sense

[malcalakovalski]

Would it be possible to do the same for plot.tag.position? If the tag position is set to "topleft" it's also misaligned with the title.

library(ggplot2)

ggplot(data = diamonds, mapping = aes(x = carat, y = price, color = cut)) +
  geom_point() +
  labs(title = "A plot title",
       tag = 'Figure 1') +
  theme(plot.title.position = "plot",
        plot.tag.position = 'topleft')

[clauswilke]

@malcalakovalski Use plot.tag.position = c(0, 1):

library(ggplot2)

ggplot(data = diamonds, mapping = aes(x = carat, y = price, color = cut)) +
  geom_point() +
  labs(
    title = "A plot title",
    tag = "Figure 1"
  ) +
  theme(
    plot.title.position = "plot",
    plot.tag.position = c(0, 1),
    plot.tag = element_text(hjust = 0, vjust = 1)
  )

[malcalakovalski]

@clauswilke Thank you! But is there a way to do that such that the tag is above the title?

[clauswilke]

You could add some top margin to the title with plot.title = element_text(margin = margin(16, 0, 0, 0)). Not sure if there's a different, more elegant approach.

[malcalakovalski]

That works for my current purposes. Thank you!

[brunomioto]

Is there a workaround for it?

[teunbrand]

This should not be terribly difficult to implement, as Hadley already left the solution in his comments:

ggplot2/R/plot-build.r

Lines 232 to 234 in 0d0de37

	panel_dim <- find_panel(plot_table)
	# for align-to-device, use this:
	# panel_dim <- summarise(plot_table$layout, t = min(t), r = max(r), b = max(b), l = min(l))

However, this brings us to a harder problem: what would the name of this argument be?