How can I change the colour line size and shape size in the legend independently?

Question

I have a line plot where I combine a colour and shape into the same legend. I want the dot size in the legend to be larger and the line in the legend to remain the same so that the shape is more clear.

From How to increase the size of points in legend of ggplot2? I understand that the dot size can be changed with + guides(colour = guide_legend(override.aes = list(size=10))), however this also changes the line size. If I add guides(shape = guide_legend(override.aes = list(size=4)),color = guide_legend(override.aes = list(size=1))) it says `Duplicated override.aes is ignored and only the second size is used.

Example code:

example <- data.frame(a=c(1,2,3,1,2,3), b=c(0.1,0.2,0.3,0.4,0.5,0.6), c=c('a','a','a','b','b','b'))

ggplot(example, aes(x=a, y=b, color=c, shape=c))+
  geom_line()+
  geom_point()+
  scale_colour_manual(name="title", breaks=c("a","b"),
                      labels=c("label1","label2"),
                      values=c("#e41a1c", "#377eb8"))+
  scale_shape_manual(name="title", breaks=c("a","b"),
                     labels=c("label1","label2"),
                     values=c(15, 16))+
  guides(shape = guide_legend(override.aes = list(size=4)),
         color = guide_legend(override.aes = list(size=1)))

example plot

score 3 · Accepted Answer · answered Apr 08 '20 at 08:34

The layer() function that ggplot uses under the hood has a key_glyph argument that you can provide a custom function to. You can use this to make the points larger, but not the lines. If you need custom line adjustments, you can write a similar function wrapping draw_key_path().

library(ggplot2)

example <- data.frame(a=c(1,2,3,1,2,3), b=c(0.1,0.2,0.3,0.4,0.5,0.6), c=c('a','a','a','b','b','b'))

large_points <- function(data, params, size) {
  # Multiply by some number
  data$size <- data$size * 2
  draw_key_point(data = data, params = params, size = size)
}

ggplot(example, aes(x=a, y=b, color=c, shape=c))+
  geom_line()+
  geom_point(key_glyph = large_points)+
  scale_colour_manual(name="title", breaks=c("a","b"),
                      labels=c("label1","label2"),
                      values=c("#e41a1c", "#377eb8"))+
  scale_shape_manual(name="title", breaks=c("a","b"),
                     labels=c("label1","label2"),
                     values=c(15, 16))

^{Created on 2020-04-08 by the reprex package (v0.3.0)}

How can I change the colour line size and shape size in the legend independently?

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