[R-sig-Geo] count overlapping polygons

[Camilo Sanin]

Dear R-sig-Geo users,

I was wondering if any of you knew how to count the number of features  
in a given shapefile that overlap each feature of another shapefile  
(such as a grid). This is sort of what the "count overlapping  
polygons" extension for ArcView (http://www.mosaic-conservation.org/gis/overlap.html 
) does, only that in this case I would like to count features with a  
duplicated value in a certain column on the attribute table only once.

thanks in advance for your help,

Camilo Sanin