group by two columns in ggplot2

Question

Is it possible to group by two columns? So the cross product is drawn by geom_point() and geom_smooth()?

As example:

frame          


        

Answer 1

Why not just paste those two columns together and use that variable as groups?

frame$grp <- paste(frame[,1],frame[,2])

A somewhat more formal way to do this would be to use the function interaction.