I have a SpatialGridDataFrame in R and want to plot just one of its attributes as as polygons in a GIS. There seems to be no simple way to do this. 

The situation is complicated by the fact that the variable I want to export is not numeric so I can't just convert it to a raster and export it. It seems like I have to have the grid file converted to polygons in R and then export the polygons into a GIS format.

I've tried Grid2Polygons package but I don't seem to be able to carry across the attributes.