Plotting discrete and continuous scales in same ggplot

Question

I would like to plot some different data items using ggplot2, using two different colour scales (one continuous and one discrete from two different df\'s). I can plot either exa

Answer 1

The problem isn't so complicated as you might think. In general, you can only map an aesthetic once. So calling scale_colour_* twice makes no sense to ggplot2. It will try to force one into the other.

You can't have multiple colour scales in the same graph, regardless of whether either one is continuous or discrete. The package author has said that they have no intention of adding this, either. It is rather complicated to implement and would make it too easy to make incredibly confusing graphs. (Multiple y axes will never be implemented for similar reasons.)