In R using the raster package, you can create box plots from two rasters (x and y) like so:
x = Raster* object y = If x is a RasterLayer object, y can be an additional RasterLayer to group the values of x by 'zone'
Which works perfectly when I want to group the values of x by all the classes in my thematic raster y.
But if I only want to group the values in x by a subset of the thematic classes in y, is there a way to do this? I could replace any values in y outside the values I am interested with NODATA values, but I was hoping there a cleaner, simpler method.