Use image instead of labels in ggplot2 legend

ggplot2, graphing, r

Solution

You're much better off using `ggsave` to save the figure as a `eps` or `svg`, then opening it in Illustrator (or open source equivalent) and replacing the legend with the images. If you're really dead set on doing it all in R, you can use `annotation_raster` in the current `ggplot2` and add in some text next to it using `geom_text`. Here is a rough attempt:

set.seed(10)
library(ggplot2) 
library(RCurl)
library(png)
df <- data.frame(animal = sample(c("sharks", "tigers"),20, rep=T), time=1:20, 
                 scariness = rnorm(20)*-20)

shark <- readPNG(getURLContent("http://i.imgur.com/EOc2V.png"))
tiger <- readPNG(getURLContent("http://i.imgur.com/zjIh5.png"))

ggplot(df, aes(time, scariness, group = animal, color = animal)) + 
geom_line(show_guide = FALSE) +
 annotation_raster(tiger, xmin = nrow(df)-1, xmax = nrow(df), 
    ymin = max(df$scariness)-(.05*max(df$scariness)), 
    ymax = max(df$scariness), interpolate = T) +
 annotation_raster(shark, xmin = nrow(df)-1, xmax = nrow(df), 
    ymin = max(df$scariness)-(.1*max(df$scariness)), 
    ymax = max(df$scariness)-(.05*max(df$scariness)), interpolate = T)

Problem

I have a plot in ggplot2 with, say, 2 lines, and in the legend I have "Sharks" and "Tigers". Is there a way I could have shark/tiger images appear in the legend instead of that text?

Original source