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I have a raster as a RasterLayer (raster) and a polygon layer (bound) with 38 individual polygons as a SpatialPolygonsDataFrame. I used the polygon to mask from a larger raster. Each polygon contains either 4 or 5 individual pixels.

I want to extract the cell values by the name of each individual polygon. I know I can do this:

v <- extract(raster, bound)

v.counts <- lapply(v,table)

But this ends up looking like this:

> v.counts

[[1]]

0.0463505908846855 0.0503523759543896 0.0531094446778297 0.0665162950754166 
             1                  1                  1                  1 

[[2]]

0.0755022615194321 0.0766473188996315 0.0860441327095032  0.612392961978912  
0.689212620258331 
             1                  1                  1                  1                  1 

Is there a different way to do this or a way to get the name field associated with the bound polygon to appear in the parentheses in the above output? For example [[Reservoir A]] instead of [1]?

Could this have anything to do with how the individual polygons are named in the shapefile? For example if you view the "polygons" portion in view, each polygon is named [1], [[2]] etc. :

example

Is there a way to just simply change the name of the polygon to get my intended output?

  • Why are you doing and showing the output from table? Doesn't the extract do what you want? Possibly names(v.counts) = bounds$NAME will do the renaming... – Spacedman Jan 6 at 22:27
  • You can use v <- extract(raster, bound, df = TRUE) to get a data.frame back instead of a list. It includes an ID field (ordered based on the order of original polygons) that can be used to "join back" to the other attributes of the shape. – lbusett Jan 6 at 22:48

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