Andrew, this is a bug; thanks for the clear report.
the code in cvs has it corrected, meaning that the next CRAN release should work. I also noted that fn is ignored for grids; it should work there too, so that the lengthy g.poly <- as(g, "SpatialPolygons") wouldn't be required. This still needs some work. -- Edzer Andrew James Hoskins wrote: > Hi all, > > I'm trying to get the sum of value z for all points that fall within a grid > square. I've been trying to use the overlay function on a grid converted to > polygons, however, it returns the sum of the coordinates and the z values, > how can I have it return only the sum of z? > Also, once I have the sum of z how then can I assign that to it's > corresponding grid square? > > ## Example code > > g <- GridTopology(c(-10,-10), c(1,1), c(21,21)) > g.poly <- as(g, "SpatialPolygons") > > x <- c(1:10,1:10) > y <- c(10:1,10:1) > z <- 1:20 > > xyz <- SpatialPointsDataFrame(cbind(x,y),data.frame(z)) > > ol <- overlay(xyz, g.poly, fn=sum) > > > Thanks in advance. > > Andrew. > > > > _______________________________________________ R-sig-Geo mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
