ggplot legend not working with scale_colour_manual

Question

I know an identical question has been asked earlier. ggplot legend - scale_colour_manual not working

But the question involves a somewhat complicated dataset than wh

Answer 1

You have to use show_guide=TRUE in geom_vline (defaults to FALSE):

p <- data.frame(a = runif(10, 1, 2))
ggplot(data=p, aes(x=a)) +
  geom_histogram() +
  geom_vline(aes(xintercept=mean(a), colour="mea"), show_guide=TRUE) +
  geom_vline(aes(xintercept=median(a), colour="med"), show_guide=TRUE) +
  scale_colour_manual(name="Statistic",
                      values=c("med"= "red", "mea"="green"))