ggplot2, legend on top and margin

Question

Consider the following:

library(ggplot2) library(grid) ggplot(diamonds, aes(clarity, fill=cut)) +    geom_bar() +      theme(     plot.margin=unit(x=c(0,0,0,0),units="mm"),     legend.position="top",     plot.background=element_rect(fill="red")) +   guides(fill=guide_legend(title.position="top")) 

The output of that looks something like this: In the context of plot.margin=unit(x=c(0,0,0,0),units="mm") there's an unseemly amount of white (red) space above the legend. Does anyone know how to remedy that?

Thanks for any hint.

Sincerely, Joh

Answer 1

Like you said, I can't see it in your example, but I'm guessing the margin is of the legend itself. You can eliminate the margin around the legend itself by adding:

+ theme(legend.margin=margin(t = 0, unit='cm')) 

This applies to ggplot2 v2.1.0 or higher. Note that, at least for now, the old solution still works as well:

+ theme(legend.margin=unit(-0.6,"cm")) # version 0.9.x 

Answer 2

If I exaggerate the margins for more visibility, and run showViewports, I get the following:

p + guides(fill=guide_legend(keyheight=unit(1,"cm"))) + theme(plot.margin=unit(c(1,1,1,1),"cm")) showViewport(col="black",label=TRUE, newpage=TRUE, leaves=FALSE) 

from which it would appear that the non-existent title is somehow taking space.

Edit: nope, it's just an unfortunate overlap of the labels. It's not the title.

Let's look at the legend itself, which seems to be causing the problem.

library(gtable) g = ggplotGrob(p) leg = gtable_filter(g, "guide") plot(leg) leg$heights # sum(0.5lines, sum(1.5mm, 10mm, 0mm, 1.5mm), 0.5lines)+0cm grid.rect(height=leg$heights)  grid.rect(height=leg$heights - unit(1,"line"), gp=gpar(lty=2)) 

so, indeed, it's the legend that's adding some margins (0.5 + 0.5 = 1 line in total). I reckon it's a missing guide.margin option in the theme, that is being replaced by a default value of half a line.