I would argue (somewhat emphatically) that the parallel facilities you are looking at are absolutely not for `for` loops. `for` loops are a control structure native to imperative programming and, as such, are inherently stateful. This provides many advantages, but easy parallelization is absolutely not one of them. Rather consider R as a functional language and the appropriate "control structure" is the Map(), most famously of MapReduce, but also inherent in R's *apply() family of functions. The careful reader will note that here is where parallelization is exposed. By being state-free, there's no inherent sequentiality and, consequently, no barriers to parallel computing.
For a somewhat concrete example consider what it would take to do a state-dependent simulation (like a gibbs sampler) in parallel: it is, to my mind, quite non-trivial. Compare this to the question of doing column sums of a matrix in parallel -- effectively trivial. The parallelization afforded by R is of that second sort. A red herring in this discussion is the foreach() formalism, but a moment's thought suggests to me that foreach() is much closer to Map() than to for(). Best, Michael On Sun, Jun 17, 2012 at 1:23 PM, Gary Dong <pdxgary...@gmail.com> wrote: > Thanks for all replied. > > I read the introduction of R parallel. Is it for loops only? > > Gary > > > On Sun, Jun 17, 2012 at 10:04 AM, R. Michael Weylandt > <michael.weyla...@gmail.com> <michael.weyla...@gmail.com> wrote: >> >> Take a look at the parallel package which ships with all current versions >> of R. >> >> Michael >> >> On Jun 17, 2012, at 11:39 AM, Gary Dong <pdxgary...@gmail.com> wrote: >> >> > Dear R users, >> > >> > I'm wonder if there is a easy way to make R use multi-CPUs on my >> > computer. >> > My computer has four CPUs but R uses only one. Thanks. >> > >> > Gary >> > >> > [[alternative HTML version deleted]] >> > >> > ______________________________________________ >> > 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. > > ______________________________________________ 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.
