3 messages · Barry Rowlingson, Philippi, Tom, Robert J. Hijmans
Dear Nevil Amos, Maybe the function 'reclassify' in the raster package is what you are looking for.
This should be trivially parallelizable, so if you have a cluster handy there should be a way to split the raster and farm out the task amongst the cluster. Don't have a cluster? Rent one from Amazon. Barry
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Nevil, It seems to me that replacing numbers using a lookup table of 197000 rows x 80 reclass values for a (not very large) raster of 197000 values can be solved more easily. Unfortunately, you did not provide code that generates example data; please do so in the future, now you leave us guessing. Presumably the lookup table column 'Value' is a cell number. Is so, and if they are sorted, perhaps you can simply do: b <- brick(r, nl=83) b <- setValues(b, mydataOut[,5:88]) Robert
A couple of hints: asc files are very slow to process in R. I would write it back to the disk as either a native grd, or even geoTiff, before reclassifying (in my experience, perhaps a 100x increase in throughput). If you have enough memory and are running 64-bit R, load the raster into memory rather than run it from the disk. If you have a quad (or more) core cpu, look at using clusterR() in raster for simple (snow) parallel processing. ?clusterR even has an example with reclassify. That can get you another 2x or 3x speedup. If all that fails, what Barry said, although for me, the upload/download time for a cloud solution would take longer than computing on my circa 2007 desktop (slow quad core with 20GB RAM). Tom On Fri, Sep 13, 2013 at 1:37 AM, Barry Rowlingson < b.rowlingson at lancaster.ac.uk> wrote:
On Fri, Sep 13, 2013 at 8:06 AM, Lionel Hertzog <s6lihert at uni-bonn.de> wrote:
Dear Nevil Amos, Maybe the function 'reclassify' in the raster package is what you are looking for.
This should be trivially parallelizable, so if you have a cluster handy there should be a way to split the raster and farm out the task amongst the cluster. Don't have a cluster? Rent one from Amazon. Barry
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