[R] parallel computation with plyr 1.2.1

[Dylan Beaudette]

On Thursday 16 September 2010, David Winsemius wrote:
> On Sep 16, 2010, at 1:11 PM, Dylan Beaudette wrote:
> > Hi,
> >
> > I have been trying to use the new .parallel argument with the most
> > recent
> > version of plyr [1] to speed up some tasks. I can run the example in
> > the NEWS
> > file [1], and it seems to be working correctly. However, R will only
> > use a
> > single core when I try to apply this same approach with ddply().
> >
> > 1. http://cran.r-project.org/web/packages/plyr/NEWS
> >
> > Watching my CPUs I see that in both cases only a single core is
> > used, and they
> > take about the same amount of time. Is there a limitation with how
> > ddply()
> > dispatches parallel jobs, or is this task not suitable for parallel
> > computing?
>
> Was this done in a GUI? The registerDoMC help page says:
> "...  registerDoMC, should not be used in a GUI environment, because
> multiple processes then share the same GUI."
>
> I, by the way, before reading the above ran it on a Mac with the GUI
> with cores=4 and did experience a slightly decreased time. The non-GUI
> restriction may also explain why I couldn't get the multicore package
> to do anything useful when I tried it in the past.

Interesting. I did not run it from within a GUI, rather from a linux terminal. 
It is a little sad that doMC will not work when called from the GUI-- as most 
of the users that I am currently developing a package for will be constrained 
to windows.

Dylan

-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341