Points fill in legend

[DrrDom]

I noticed that if I use fill with geom_point I have to manually set the shape of the legend point to make the fill color visible

library(ggplot2)

set.seed(42)
d <- data.frame(x = rnorm(12), y = rnorm(12), 
                shape = rep(LETTERS[1:4], each = 3), 
                fill = rep(letters[1:3], 4))

ggplot(d, aes(x = x, y = y, shape = shape, fill = fill)) +
  geom_point(size = 3) +
  scale_shape_manual(values = 21:25) +
  theme(legend.box = "horizontal")

ggplot(d, aes(x = x, y = y, shape = shape, fill = fill)) +
  geom_point(size = 3) +
  scale_shape_manual(values = 21:25) +
  guides(fill = guide_legend(override.aes=list(shape=21))) +
  theme(legend.box = "horizontal")

It seems to be reasonable to change the default behavior in such cases, because it is not obvious and requires search for a solution over the internet.

[thomasp85]

Yeah, this is clearly a bug

[thomasp85]

Hmm... this is actually not easy to fix. There is no way in the legend key drawing code where it is given that the values comes from the defaults or not.

Because of this we cannot selectively use another shape if a fill is given... @yutannihilation, @clauswilke, @hadley any good ideas?

[thomasp85]

The best approach (but also rather involved) is to modify

ggplot2/R/guide-legend.r

Lines 267 to 276 in 668a51e

	data <- tryCatch(
	layer$geom$use_defaults(guide$key[matched], params, modifiers),
	error = function(...) {
	warn("Failed to apply `after_scale()` modifications to legend")
	layer$geom$use_defaults(guide$key[matched], params, list())
	}
	)
	} else {
	data <- layer$geom$use_defaults(NULL, layer$aes_params)[rep(1, nrow(guide$key)), ]
	}

So that instead of using geom$use_defaults() it would use another another function that fills in default values from values actually used by the layer... This would require the layer to keep track of aesthetic values used and will have other downsides in that e.g. a red glyph colour would be used in the shape legend instead of the more neutral black

All in all I'm not sure this is worth "fixing" since it would open up other issues

[hadley]

Could we change the shape if colour is constant and fill is varying?

[thomasp85]

The keys are created one by one, so there is no concept of constant vs varying...

Another issue is that if a global fill is set, e.g. to fill a boxplot and the points are drawn with the default 19 shape you don't want the legend to show points with a coloured center

[clauswilke]

My opinion: When people venture into shapes 21-25 they're accepting that they'll have to deal with minor inconveniences such as this one. It's an advanced use case that can lead to unintuitive results on occasion.

[hadley]

Yeah, in that case I'm with @clauswilke.

[thomasp85]

Ok, let's close it