rmflight - 8 months ago 54
R Question

# Overlapped density plots in ggplot2

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:

``````vec1 <- data.frame(x=rnorm(2000, 0, 1))
vec2 <- data.frame(x=rnorm(3000, 1, 1.5))
ggplot() + geom_density(aes(x=x, colour="red"), data=vec1) +
geom_density(aes(x=x, colour="blue"), data=vec2)
``````

Then I thought I should do this:

``````vec1 <- data.frame(x=rnorm(2000, 0, 1))
vec2 <- data.frame(y=rnorm(3000, 1, 1.5))
ggplot() + geom_density(aes(x=x, colour="red"), data=vec1) +
geom_density(aes(x=y, colour="blue"), data=vec2)
``````

Neither of these quite work, because the colors get mixed up.

Based on another solution I found in StackOverflow 1 2, I realized I should try this:

``````vec1 <- data.frame(x=rnorm(2000, 0, 1), grp="vec1")
vec2 <- data.frame(x=rnorm(3000, 1, 1.5), grp="vec2")
allDat <- rbind(vec1, vec2)

ggplot(allDat, aes(x, colour=grp)) + geom_density()

ggplot(allDat, aes(x, colour=grp)) + geom_density() +
scale_colour_manual(values=c("green", "blue"))

ggplot(allDat, aes(x, colour=grp)) + geom_density() +
scale_colour_manual(values=c(vec2="green", vec1="blue"))
``````

OK, I solved my original problem. But is there a way to do something akin to the first one I tried above? From the way things are worded in the
`ggplot`
documentation, I would have thought so. Appreciate any suggestions.

Everything will work fine if you move the assignment of the `colour` parameter out of `aes()`.
``````vec1 <- data.frame(x=rnorm(2000, 0, 1))