Error when using %dopar% instead of %do% in R (package doParallel)

Question

I\'ve come up with a strange error. Suppose I have 10 xts objects in a list called data. I now search for every three combinations using

   data_names <-          


        

Answer 1

The problem is likely that you haven't called library(xts) on each of the workers. You don't say what backend you're using, so I can't be 100% sure.

If that's the problem, then this code will fix it:

list <- foreach(i=1:ncol(combs)) %dopar% {
    library(xts)
    tmp_triple <- combs[,i]

    p1<-data[tmp_triple[[1]]][[1]]
    p2<-data[tmp_triple[[2]]][[1]]
    p3<-data[tmp_triple[[3]]][[1]]

    data.merge <- merge(p1,p2,p3,all=FALSE)
}

Answer 2

A better solution rather than explicitly loading the libraries within the function would be to utilise the .packages argument of the foreach() function:

list <- foreach(i=1:ncol(combs),.packages=c("xts","zoo")) %dopar% {
    tmp_triple <- combs[,i]

    p1<-data[tmp_triple[[1]]][[1]]
    p2<-data[tmp_triple[[2]]][[1]]
    p3<-data[tmp_triple[[3]]][[1]]

    data.merge <- merge(p1,p2,p3,all=FALSE)
}

Answer 3

Quick fix for problem with foreach %dopar% is to reinstall these packages:

install.packages("doSNOW")

install.packages("doParallel") 

install.packages("doMPI")

These are responsible for parallelism in R. Bug which existed in old versions of these packages is now removed. It worked in my case.