[R-sig-Geo] [raster] formal way of addressing specific layer in RasterStack?

[dcd]

Just curious if this is the most optimal way of addressing a specific layer
in a RasterStack:

-RasterStack with 14 layers called "stack"
-polygon layer called "sites"

# extract cell values from layer 2 of "stack" RasterStack using "sites"
polygon
extract_stack_sites<-extract(stack at layers[[2]], sites))

# extract summary stats (mean) for each polygon
extract_stack_sites_mean<-unlist(lapply(extract_stack_sites, function(x) if
(!is.null(x)) mean(x, na.rm=TRUE) else NA ))

The above works, but perhaps there's a more elegant solution, especially if
dealing with a range, or subset of layers within a RasterStack?

Cheers



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