Overlapped density plots in ggplot2

Question

Imagine I have two vectors each of different length. I want to generate one plot with the density of both vectors overlaid. What I thought I should do is this:

Answer 1

Everything will work fine if you move the assignment of the colour parameter out of aes().

vec1 <- data.frame(x=rnorm(2000, 0, 1))
vec2 <- data.frame(x=rnorm(3000, 1, 1.5))

library(ggplot2)

ggplot() + geom_density(aes(x=x), colour="red", data=vec1) + 
  geom_density(aes(x=x), colour="blue", data=vec2)