在ggplot2中微调传奇键的麻烦

Question

I'm trying to have legend keys match exactly the plot using the theme() and guides() functions.

Starting with this plot:

library(ggplot2)
data(mpg)

mpg$year <- as.numeric(mpg$year)
means <- tapply(mpg$displ, list(mpg$year), FUN = mean)
means <- as.data.frame(means)
means$year <- as.numeric(row.names(means))
names(means)[1] <- "displ"

p1 <- 
  ggplot(mpg, aes(x = year, y = displ)) +
  geom_jitter(aes(color = "points")) +
  geom_errorbar(data = means, aes(ymin = displ, ymax = displ, 
    color = "mean")) +
  scale_x_continuous(breaks = c(1998, 2008))

p1

I get a plot where I can modify legend keys using:

p1 + theme(legend.key = element_rect(fill = NA), 
legend.title = element_blank()) + 
guides(color = guide_legend(override.aes = 
list(shape=c(NA, 16), linetype=c(1, 0), fill = c(NA, NA))))

Getting the desired result:

However, when the plot also contains geom_ribbon() the same method fails:

p2 <- 
  ggplot(mpg, aes(x = year, y = displ)) +
  geom_jitter(aes(color = "points")) +
  geom_ribbon(aes(ymin = 3, ymax = 4, color = "ribbon"), 
    fill = "green", alpha = 0.5) +
  geom_errorbar(data = means, aes(ymin=displ, ymax=displ, 
    color="mean")) +
  scale_x_continuous(breaks = c(1998, 2008))

p2 + theme(legend.key = element_rect(fill = NA), 
  legend.title = element_blank()) + 
  guides(color = guide_legend(override.aes = 
    list(shape=c(NA, 16, NA), linetype=c(1, 0, 0), 
    fill = c(NA, NA, "green"))))

To be clear: I want the legend key representing the mean to show as just a straight red line, like in the first plot, no border, no diagonal.

(I realize I could use stat_summary() instead of creating a separate dataframe, but that won't work for my actual project).

Thanks for any advice,

Lasse

---

Answer 1

This might be a bit of a hack, but I removed the legend from geom_ribbon and added the ribbon color as a point type (pch = 15) in the legend. The colors are not perfect yet, but I bet you can manage.

p2 <- 
  ggplot(mpg, aes(x = year, y = displ)) +
  geom_jitter(aes(color = "points")) +
  geom_ribbon(aes(ymin = 3, ymax = 4, color = "ribbon"), 
              fill = "green", alpha = 0.5, show.legend = FALSE) +
  geom_errorbar(data = means, aes(ymin=displ, ymax=displ, 
                                  color="mean")) +
  scale_x_continuous(breaks = c(1998, 2008))

p2 + theme(legend.key = element_rect(fill = NA), 
           legend.title = element_blank()) + 
  guides(color = guide_legend(override.aes = 
                                list(shape=c(NA, 16, 15), linetype=c(1, 0, 0), 
                                     color = c("red", "green", "green"),
                                     alpha = c(1,1,.5),
                                     size = c(1,2,6))))