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

Actually, you'll need to identify the values of the foreach loop in the for
loop for it to work...

require(doParallel)
require(foreach)
set.seed(666)
xyz<-as.data.frame(cbind(x=rep(rpois(50000,10),2)+1,
y=rep(rpois(50000,10),2)+1,z=round(runif(100000, min=-3, max=40),2)))
xyz$mins<-rep(NA, nrow(xyz))
xyz[order(xyz[,1],xyz[,2], xyz[,3]),]->xyz

cl<-makeCluster(4)  #adjust to your cluster number
registerDoParallel(cl)
test<-foreach(i=unique(xyz[,1]), .combine=rbind, .verbose=T) %dopar% {
     for(j in unique(xyz[xyz[,1] == i,2] )) {                                   
# here ensure you pass on the right data
         xyz[xyz[,2] == j & xyz[,1] == i ,4]<-min(xyz[xyz[,2] == j &
xyz[,1] == i,3])  # otherwise there are inf values here
        nr=nrow(xyz[xyz[,2] == j & xyz[,1] == i ,4])
        }
        return(xyz[xyz[,1]== i,])  # you must return what you are farming out...
}
test[1:15,]
stopCluster(cl)


XXXXXXXXXXXXXXXXXXXXX Herry wrote XXXXXXXXXXXXXXXXXX

Hiya,

This now works...

test<-foreach(i=unique(xyz[,1]), .combine=rbind, .verbose=T) %dopar% {
         for( j in unique(xyz[,2])) {
         xyz[xyz[,2] == j & xyz[,1] == i ,4]<-min(xyz[xyz[,2] == j &
xyz[,1] == i,3])
        nr=nrow(xyz[xyz[,2] == j & xyz[,1] == i ,4])
        }
        return(xyz[xyz[,1]== i,])  # you must return what you are farming out...
}
head(test)