Plot with darker color for denser areas and transparent color for less dense areas

Question

How can I make a plot in R with ggplot2 that is darker where there are more points and more transparent where there are less points? I tried making a geom_hex plot with a gradient but it is ignoring alpha values.

Answer 1

set.seed(101)
dd <- data.frame(x=rnorm(3000),y=rnorm(3000))
library(ggplot2); theme_set(theme_bw())

Set alpha on points, natural overlap:

ggplot(dd,aes(x,y))+geom_point(alpha=0.1,size=8)

(made points larger to get overlap)

Or:

ggplot(dd,aes(x,y))+stat_density_2d(geom="raster",
               aes(alpha = ..density..), contour = FALSE)+
     scale_x_continuous(expand=c(0,0))+
     scale_y_continuous(expand=c(0,0))

Still working on geom_hex ... I can't actually figure out how to do this ... aes(alpha=..count..) seems as though it should work based on R ggplot geom_hex alpha transparency , but ??

 ## fails with ggplot 2.1.0 ... ?
 ggplot(dd,aes(x,y))+
     geom_hex(aes(alpha=log(..count..)))