R help - Aug 2016 - foreach {parallel} nested with for loop to update data.frame column

Hi List,

Trying to update a data.frame column within a foreach nested for loop

### trial data
set.seed(666)
xyz<-as.data.frame(cbind(x=rep(rpois(5000,10),2)+1,
y=rep(rpois(5000,10),2)+1,z=round(runif(10000, min=-3, max=40),2)))
xyz$mins<-rep(NA, nrow(xyz)) 

cl<-makeCluster(16)  #adjust to your cluster number
registerDoParallel(cl)

counter=0
foreach(i=unique(xyz[,1]), .combine=data.frame, .verbose=T) %dopar% {
        for( j in unique(xyz[,2])) {
                xyz[xyz[,2] == j ,4]<-min(xyz[xyz[,2] == j ,2]) 
        }

}

stopCluster(cl)

This is obviously not working. Any hints?

Thanx
Herry

Hi

I may be completely wrong but isn't it work for ave? With your example I get
> fac<-interaction(xyz[,1], xyz[,2], drop=TRUE)
> xyz[,4]<-ave(xyz$z, fac, FUN= min)
> head(xyz)
   x  y     z  mins
1 13 15  1.97 -2.91
2 17  9 14.90 -2.81
3  9 10 34.68 -1.97
4 17  6  4.26 -2.63
5  3 12  0.12  0.12
6 19 11  7.91  7.91
>
Cheers
Petr

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of
> Alexander.Herr at csiro.au
> Sent: Thursday, August 4, 2016 3:32 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] foreach {parallel} nested with for loop to update data.frame
> column
>
> Hi List,
>
> Trying to update a data.frame column within a foreach nested for loop
>
> ### trial data
> set.seed(666)
> xyz<-as.data.frame(cbind(x=rep(rpois(5000,10),2)+1,
> y=rep(rpois(5000,10),2)+1,z=round(runif(10000, min=-3, max=40),2)))
> xyz$mins<-rep(NA, nrow(xyz))
>
> cl<-makeCluster(16)  #adjust to your cluster number
> registerDoParallel(cl)
>
> counter=0
> foreach(i=unique(xyz[,1]), .combine=data.frame, .verbose=T) %dopar% {
>         for( j in unique(xyz[,2])) {
>                 xyz[xyz[,2] == j ,4]<-min(xyz[xyz[,2] == j ,2])
>         }
>
> }
>
> stopCluster(cl)
>
> This is obviously not working. Any hints?
>
> Thanx
> Herry
>
> ______________________________________________
> 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.
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