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

You can do this. You need to tell grid graphics to overlay one plot on top of the other. You have to get margins and spacing etc, exactly right, and you have to think about the transparency of the top layers. In short... it's not worth it. As well as possibly making the plot confusing.

However, I thought some people might like a pointer on how to acheive this. N.B. I used code from this gist to make the elements in the top plot transparent so they don't opaque the elements below:

grid.newpage()
pushViewport( viewport( layout = grid.layout( 1 , 1 , widths = unit( 1 , "npc" ) ) ) ) 
print( p1 + theme(legend.position="none") , vp = viewport( layout.pos.row = 1 , layout.pos.col = 1 ) )
print( p2 + theme(legend.position="none") , vp = viewport( layout.pos.row = 1 , layout.pos.col = 1 ) )

See my answer here for how to add legends into another position on the grid layout.