Using override.aes() in ggplot2 with layered symbols (R)

Question

I recently asked a question here which allowed me to add borders to geom_point()s in ggplot2 with customizable colors and thickness. Admittedly, it's a bit of a hack and I'm now having some trouble which may be a result of this. The borders are generated by layering two geom_point()s, one of which is the color of the border that I want and which is slightly larger than the geom_point() which provides the "fill". A reproducible example here:

require('ggplot2')

values <- rnorm(n = 10, mean = 1, sd = 0.5) + c(1:10)

df <- data.frame(id = rep(c('hq', 'lq'), each = 5),
                 values = values,
                 period = rep(c(1:5), 2))

plot <- 
    ggplot(df, aes(x = period,
                   y = values,
                   group = id,
                   shape = id,
                   color = id)) +
    geom_line(color = 'gray40') +
    geom_point(color = 'gray24',
               size = 4) +
    geom_point(size = 3) +
    guides(shape = guide_legend(override.aes = list(size = 5))) +
    scale_color_manual(values = c('lightskyblue1', 'lightpink'),
                       labels = c('HQ', 'LQ')) +
    scale_shape_manual(values = c(15, 17, 0, 2),
                       labels = c('HQ', 'LQ')) +
    theme_bw()

Because I would like the legend symbols to be larger than the plot symbols, I've used override.aes(). However, this means that the "borders" I've created do not appear in the legend:

Is there some way to give multiple size arguments to override.aes() so that the layering I've used in the plot is left intact in the legend (i.e. the legend symbols also contain the "borders")?

Answer 1

You can do this with a single call to geom_point if you use a point-marker with both a border and a fill (pch values from 21 through 25; see ?pch). Then, you can set the size of the legend markers with override.aes and the borders and fill will always appear correctly. For example:

ggplot(dat, aes(x = period,
                y = values,
                group = id,
                shape = id,
                fill=id)) +
  geom_line(color = 'gray40') +
  geom_point(size=4) +
  guides(shape = guide_legend(override.aes = list(size = 5))) +
  scale_fill_manual(values = c('lightskyblue1', 'lightpink'),
                    labels = c('HQ', 'LQ')) +
  scale_shape_manual(values = c(22,24),   # These are the marker shapes
                     labels = c('HQ', 'LQ')) +
  theme_bw()

This results in a black border for the point markers (the default value, but you can change it) and the fill colour you specify.

UPDATE: In response to your comment, here's how to get the black border on the legend markers without any other changes to your original code:

  guides(shape = guide_legend(override.aes = 
                                list(size = 5, shape=c(22,24), 
                                     colour="black", 
                                     fill=c('lightskyblue1', 'lightpink')))) +