how to create this figure with 3 labels in R? (showing different shades)

Question

I wonder how to integrate three variables in one figure as the example in the attached picture. How to realize that the "number of pairs" are denoted by different shades?

Answer 1

set.seed(42)
DF <- data.frame(x=runif(1e5), y=rpois(1e5,20))

library(ggplot2)
ggplot(DF, aes(x,y)) + stat_bin2d()