Iterate features on SpatialPolygonsDataFrame in R

Question

I have a SpatialPolygonsDataFrame object. Is there way to use apply on this object rather than using a for loop to iterate features in this object?

Answer 1

You probably want to iterate over the polygons.

As an example, start with this grid taken from the manual page (but cut down in size):

library(sp)
grd <- GridTopology(c(1,1), c(1,1), c(3,3))
polys <- as.SpatialPolygons.GridTopology(grd)
centroids <- getSpPPolygonsLabptSlots(polys)
x <- centroids[,1]
y <- centroids[,2]
z <- 1.4 + 0.1*x + 0.2*y + 0.002*x*x
data <- SpatialPolygonsDataFrame(polys, 
             data=data.frame(x=x, y=y, z=z, row.names=getSpPPolygonsIDSlots(polys)))

Here sapply is used to create a vector of the polygon identifiers and print it out:

(ids <- sapply(data@polygons, function(p) p@ID))