[R] Simple example for High performance computing with R?

[Martin Morgan]

On 05/29/2012 08:02 PM, Fabrice Tourre wrote:
> Dear list,
>
> I want to run two independent calculation (A, B) and then combined
> their results to do a plot in R. Before I just run calculation A
> first, then calculation B. It will take some times. I just have one
> server with multiple core. I noticed that there are some nice package
> in R for parallel calculation, such as parallel, multicore and snow.
> Also there is a book, O’Reilly – “Parallel R, Data Analysis in the
> Distributed World” book by Q. Ethan McCallum and Stephen Weston.
>
> When track into these packages, I am a little of lost because I did
> not know parallel calculation too much.
>
> Could any one can give me some example codes for my purpose? So I can
> easy follow.

Here we sleep for 20 seconds, but do it in only 5 seconds!

 > library(parallel)
 > system.time(mclapply(1:4, function(i) Sys.sleep(5), mc.cores=4))
    user  system elapsed
   0.006   0.025   5.021

Often, it is possible to use mclapply just like lapply; use the 
'parallel' library, and for single processor machines the mclapply and 
similar functions rather than parLapply and similar. This

   vignette("parallel", package="parallel")

might provide further help. Likely you will get benefit from making your 
calculation A use parallel calculations, and B use parallel calculation.

Martin

>
> Thank you very much in advance.
>
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