Extract raster values of particular polygons of a SpatialPolygonsDataFrame (indexation)

1
votes

I have a SpatialPolygonsDataFrame with 120 Polygons and some associated data. Now I’d like to extract the mean of the values on a raster within each polygon separately. I succeded in plotting individual polygons with:

plot(SpatialPolygons(SPdataframe@polygons)[i])

But it did not work to extract the values in the same manner:

extract(raster, SpatialPolygons(SPdataframe@polygons)[i],fun="mean",na.rm=TRUE,method="simple")

Can anyone explain the difference between the use of the same indexation in this two cases? What is the official way to choose particular polygons of a SpatialPolygonsDataFrame with indices?

Thank you a lot for your help in advance!

1
rgeospatialpolygonspatial

1 Answers

2
votes

The correct indexation for single polygons of a SpatialPolygonsDataFrame is: SPdataframe[i,] (Merci to R-sig_geos user Rafael Wüest)