Plotting predefined density functions using ggplot and R

Answer 1

The secret to happiness in ggplot2 is to put everything in the "long" (or what I guess matrix oriented people would call "sparse") format:

df <- rbind(data.frame(x="n",value=n),
            data.frame(x="a",value=a),
            data.frame(x="p",value=p))
qplot(value, colour=x, data=df, geom="density")

If you don't want colors:

qplot(value, group=x, data=df, geom="density")