Overlay two ggplot2 stat_density2d plots with alpha channels

Question

I want to overlay two ggplot2 plots with alpha channels in a way that the resulting image shows both datasets. This is my test data:

data = read         


        

Answer 1

You should plot both densities on the same scale:

ggplot(rbind(data.frame(data, group="a"), data.frame(data2, group="b")), 
       aes(x=x,y=y)) + 
  stat_density2d(geom="tile", aes(fill = group, alpha=..density..), 
                 contour=FALSE) + 
  scale_fill_manual(values=c("a"="#FF0000", "b"="#00FF00")) +
  geom_point() +
  theme_minimal() +
  xlim(-3.3, 3.3) + ylim(-3.3, 3.3) +
  coord_cartesian(xlim = c(-3.2, 3.2), ylim = c(-3.2, 3.2))

Otherwise you display a distorted picture of your data.