Question

I have been trying to plot simple density plots using R as:

plot(density(Data$X1),col="red")
plot(density(Data$X2),col="green")

Since I want to compare, I’d like to plot both in one figure. But ‘matplot’ doesn’t work!! I also tried with ggplot2 as:

library(ggplot2)
qplot(Data$X1, geom="density")
qplot(Data$X2, add = TRUE, geom="density")

Also in this case, plots appear separately (though I wrote add=TRUE)!! Can anyone come up with an easy solution to the problem, please?

Answer 1

In ggplot2 or lattice you need to reshape the data to seupose them.

For example :

    dat <- data.frame(X1= rnorm(100),X2=rbeta(100,1,1))
    library(reshape2)
    dat.m <- melt(dat)

Using “lattice`

  densityplot(~value , groups = variable, data=dat.m,auto.key = T)

Using “ggplot2`

 ggplot(data=dat.m)+geom_density(aes(x=value, color=variable))

EDIT add X1+X2

Using lattice and the extended formua interface, it is extremely easy to do this:

densityplot(~X1+X2+I(X1+X2) , data=dat)   ## no need to reshape data!!