I want to plot two graphs in one figure. These two graphs are plotted using ggplot2 package. Afterwards I used the following code.
grid.arrange(p1,p2,ncol=2)
My question, is there is a possibility to put in the output of grid.arrange below the two graphs subscripts like 1) and 2) or a) and b), so that helps making reference in the text easier than telling that picture on the (top) right and etc.