I'm trying to combine two shapefiles using
 zipmaps5 <- spRbind(zipmaps1,zipmaps2)

and getting the following error message
Error in spRbind(as(obj, "SpatialPolygons"), as(x, "SpatialPolygons")) :
  non-unique polygon IDs

Does anyone know how I can get rid of duplicate polygons in a shapefile?

thank you!

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