ggplot_ex.R

library(ggplot2)

df0 <- data.frame(x=rnorm(100), y=rnorm(100), grp=factor(rep(letters[1:2], each=50)))
p <- ggplot(df0, aes(x,y, colour=grp, alpha=y))
p + geom_point() 



library(RColorBrewer)

cuts <- with(df0, tapply(y, grp, cut, 3, labels=F))
df0$col <- c(brewer.pal(n=3, "Blues")[cuts$a], brewer.pal(n=3, "Reds")[cuts$b])
p2 <- ggplot(df0, aes(x,y,colour=col))
p2 + geom_point() +scale_colour_identity()