Yes, this was a little bug that will be fixed in the next release. Hadley On Thu, Sep 16, 2010 at 1:11 PM, Dylan Beaudette <debeaude...@ucdavis.edu> 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? > > Cheers, > Dylan > > > Here is an example: > > library(plyr) > library(doMC) > registerDoMC(cores=2) > > # example data > d <- data.frame(y=rnorm(1000), id=rep(letters[1:4], each=500)) > > # function that wastes some time > f <- function(x) { > m <- vector(length=10000) > for(i in 1:10000) { > m[i] <- mean(sample(x$y, 100)) > } > mean(m) > } > > system.time(ddply(d, .(id), .fun=f, .parallel=FALSE)) > # user system elapsed > # 2.740 0.016 2.766 > > system.time(ddply(d, .(id), .fun=f, .parallel=TRUE)) > # user system elapsed > # 2.720 0.000 2.726 > > > > > > -- > Dylan Beaudette > Soil Resource Laboratory > http://casoilresource.lawr.ucdavis.edu/ > University of California at Davis > 530.754.7341 > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >
-- Assistant Professor / Dobelman Family Junior Chair Department of Statistics / Rice University http://had.co.nz/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
