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@lancaster.ac.uk> wrote:

> On Fri, Sep 13, 2013 at 8:06 AM, Lionel Hertzog <s6lihert@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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