Hi. I had such great success last time, I thought I would ask for more assistance. I have an object (cb.poly) of class "SpatialPolygonsDataFrame". I would like to subset this object using a for loop that essentially loops through polygon ID from a larger list. The code looks like this:
class(cb.poly) sub.cb.poly <- cb.poly[cb.poly$Plg_id == thresh.poly.id[[687]][1,],] polygons(sub.cb.poly) dissolveset <- thresh.poly.id[[687]] ilength <- nrow(dissolveset) for (i in 2:ilength){ i <- cb.poly[cb.poly$Plg_id == thresh.poly.id[[687]][i,],] polygons(i) sub.cb.poly <- c(sub.cb.poly, i) } gg <- SpatialPolygons(sub.cb.poly,pO=1:length(sub.cb.poly)) The object thresh.poly.id[[]] is a "list" class object that holds the unique polygon names that overlapped with my tree crown polygon (thanks Roger and Greg and others). The first time I call sub.cb.poly it is a "SpatialPolygonsDataFrame" class. I then try to convert to a polygon so that after I loop it through my list of appropriate polygon IDs I can reconvert to a "SpatialPolygonsDataFrame" class. I am attempting this because after the for loop, my sub.cb.poly object is a "list" class. I could not determine how to join elements from a loop into a "SpatialPolygonsDataFrame" class, so I thought I might convert to polygons and then use SpatialPolygons function (see gg object). This is not working for me. Ultimately, I want to create an object that is a subset of my original cb.poly object so that I can do a "unionSpatialPolygons" operation to create a merged or dissolved object. Thanks for any assistance. Andrew Niccolai Doctoral Candidate Yale School of Forestry 203-432-5144 _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo