Change order of items in ggplot2 legend with combined items

Question

I use ggplot2 to draw a scatter plot which contains both a grouped and an ungrouped geom_smooth(). I would like the entry for the ungrouped smooth to appear at the top or bottom of the legend, but the legend is sorted alphabetically instead.

my.colors <- c('4' = 'red', 'f' = 'green', 'r' = 'blue', 'all' = 'black')
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(color = drv), alpha = 1/3) + theme_bw() +
  geom_smooth(aes(color = drv), method = 'lm') +
  geom_smooth(aes(color = 'all'), method = 'lm') +
  scale_color_manual(name = "Drive Types", values = my.colors)

The problem is similar to Scott's, but including a geom_blank() does not solve it. Also, including 'all' as a level in mpg$drv makes no difference.

Answer 1

Use breaks?

my.colors <- c('4' = 'red', 'f' = 'green', 'r' = 'blue', 'all' = 'black')
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(color = drv), alpha = 1/3) + theme_bw() +
  geom_smooth(aes(color = drv), method = 'lm') +
  geom_smooth(aes(color = 'all'), method = 'lm') +
  scale_color_manual(name = "Drive Types", values = my.colors, 
                     breaks=c("all", "4", "f", "r"))