2

I need to run calculations on large multi-band rasters and export a RasterBrick, and am trying to do so using the calc() function in the raster package, for the purpose of memory efficiency. The function runs fine on its own, but when I try to include it in calc(), I keep getting this error:

Error in .calcTest(x[1:5], fun, na.rm, forcefun, forceapply) : cannot use this function

How can I make this work?

Simplified code:

fn = system.file("external/test.grd", package="raster")
s = stack(fn, fn, fn, fn)

out = calc(s, fun = function(x){
  for (i in 1:nlayers(x)){
    x[[i]] = x[[i]] - cellStats(x[[i]], "min")
    x[[i]] = x[[i]]* 5
  }
  list = unstack(x)
  out = brick(list)
  return(out)
}
)

Error in .calcTest(x[1:5], fun, na.rm, forcefun, forceapply) : 
  cannot use this function
  • 3
    Get rid of your for loop, unstack and brick calls. Take a look at the help for calc and overlay. The function expects a vectorized function and not one that attempts to manipulate the raster or stack explicitly. Looping through layers in a stack is performed within calc or overlay. – Jeffrey Evans Feb 19 '17 at 16:18
  • @JeffreyEvans Looks like your comment could become an answer with no or little expansion. – PolyGeo Feb 21 '17 at 22:52
0

calc iterates through layers of a Raster Stack on its own, so a for loop and indexing is not necessary here. Removing them, as well as the unstack and brick fixes the problem.

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