21st-January-2018: R-programming and Liberapay

It would be very helpful if we could layer the Pre and Post-USD data's correlation plots, using opacity to see where there's overlap and difference. I know you can do layering with ggplot2, but I've been using corrplot for correlation plotting; I found ggcorr while googling for "layer corrplot" and it seems like something much closer to what I want!