[R-sig-Geo] subsetting a spatial polygons

[Antonio Silva]

Dear list users

I have a SpatialPolygons with several squares. How to subset it to have
only the squares between given latitudes and longitudes?

In the example

library(sp)
library(raster)
grd <-
GridTopology(cellcentre.offset=c(-47.75,-25.416667),cellsize=c(10/60,10/60),cells.dim=c(23,12))
polys <- as.SpatialPolygons.GridTopology(grd)
proj4string(polys) <- CRS("+proj=longlat +datum=WGS84")
plot(polys,axes=T)

How to select only the squares, let's say, between 24-25°S and 45-46°W?

The farthest I went was:

e <- extent(-45.9,-45.1,-24.9,-24.1) # which is not very elegant
mask <- crop(polys,e)
polys2 <- polys[mask,]
plot(polys2,add=T,col="green")

Thanks a lot. Best regards

-- 
Antônio Olinto Ávila da Silva
Instituto de Pesca (Fisheries Institute)
São Paulo, Brasil

	[[alternative HTML version deleted]]