[R] R parallel / foreach - aggregation of results

[William Dunlap]

If you return just the row that the foreach procedure produces instead of
the entire matrix containing that row and use .combine=rbind then you will
end up with the matrix of interest.  E.g.,

Simpar3a <- function (n1)
{
    L2distance <- matrix(NA, ncol = n1, nrow = n1)
    data <- rnorm(n1)
    diag(L2distance) = 0
    cl <- makeCluster(4)
    registerDoParallel(cl)
    x <- foreach(j = 1:n1, .combine = rbind) %dopar% {
        library(np)
        datj <- data[j]
        rowJ <- numeric(n1)
        for (k in j:n1) {
            rowJ[k] <- k * datj
        }
        rowJ
    }
    stopCluster(cl)
    x
}


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Sat, Aug 1, 2015 at 12:19 PM, Martin Spindler <Martin.Spindler at gmx.de>
wrote:

> Dear Jim,
>
> Thank you very much for your response. It seems to work now, but the
> return value is not the required matrix but a list of matrices (one for
> each repition j).
> Any idea how it is possible to return only the last matrix and not all?
>
> Thanks and best,
>
> Martin
>
>
>
> Gesendet: Freitag, 31. Juli 2015 um 18:22 Uhr
> Von: "jim holtman" <jholtman at gmail.com>
> An: "Martin Spindler" <Martin.Spindler at gmx.de>
> Cc: "r-help at r-project.org" <r-help at r-project.org>
> Betreff: Re: [R] R parallel / foreach - aggregation of results
>
> Try this chance to actually return values:
>
>
> library(doParallel)
> Simpar3 <- function(n1) {
>    L2distance <- matrix(NA, ncol=n1, nrow=n1)
>    data <- rnorm(n1)
>    diag(L2distance)=0
>    cl <- makeCluster(4)
>    registerDoParallel(cl)
>    x <- foreach(j=1:n1)  %dopar% {
>      library(np)
>      datj <- data[j]
>      for(k in j:n1) {
>        L2distance[j,k] <- k*datj
>      }
>      L2distance  # return the value
>    }
>    stopCluster(cl)
>    return(x)
>  }
>  Res <- Simpar3(100)
>
>
> Jim Holtman
> Data Munger Guru
>
> What is the problem that you are trying to solve?
> Tell me what you want to do, not how you want to do it.
> On Fri, Jul 31, 2015 at 8:39 AM, Martin Spindler <Martin.Spindler at gmx.de>
> wrote:Dear all,
>
> when I am running the code attached below, it seems that no results are
> returned, only the predefined NAs. What mistake do I make?
> Any comments and help is highly appreciated.
>
> Thanks and best,
>
> Martin
>
>
> Simpar3 <- function(n1) {
>   L2distance <- matrix(NA, ncol=n1, nrow=n1)
>   data <- rnorm(n1)
>   diag(L2distance)=0
>   cl <- makeCluster(4)
>   registerDoParallel(cl)
>   foreach(j=1:n1)  %dopar% {
>     library(np)
>     datj <- data[j]
>     for(k in j:n1) {
>       L2distance[j,k] <- k*datj
>     }
>   }
>   stopCluster(cl)
>   return(L2distance)
> }
>
> Res <- Simpar3(100)
>
> ______________________________________________
> R-help at r-project.org[R-help at r-project.org] mailing list -- To UNSUBSCRIBE
> and more, see
>
> https://stat.ethz.ch/mailman/listinfo/r-help[https://stat.ethz.ch/mailman/listinfo/r-help]
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html[http://www.R-project.org/posting-guide.html]
> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.

	[[alternative HTML version deleted]]