Translate for loop into parallel foreach loop in R - r

Question

I try to optimize parts of a simulation script and have parts of it run in parallel. So I discovered the foreach function.
As an example I try to have the following run in parallel
Wiederholungen<-4
assign("A",array(0,c(Wiederholungen,10,3)))
assign("B",array(0,c(Wiederholungen,10,3)))
assign("C",array(0,c(Wiederholungen,10,3)))
Old Code:
for(m in 1:Wiederholungen){
A[m,,]<-m
B[m,,]<-m
C[m,,]<-m
}
Resulting in: (for A)
A
, , 1
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 1 1 1 1 1 1 1 1 1 1
[2,] 2 2 2 2 2 2 2 2 2 2
[3,] 3 3 3 3 3 3 3 3 3 3
[4,] 4 4 4 4 4 4 4 4 4 4
, , 2
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 1 1 1 1 1 1 1 1 1 1
[2,] 2 2 2 2 2 2 2 2 2 2
[3,] 3 3 3 3 3 3 3 3 3 3
[4,] 4 4 4 4 4 4 4 4 4 4
, , 3
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 1 1 1 1 1 1 1 1 1 1
[2,] 2 2 2 2 2 2 2 2 2 2
[3,] 3 3 3 3 3 3 3 3 3 3
[4,] 4 4 4 4 4 4 4 4 4 4
This should put the value of m in the m-th row of the dataframes A,B & C. In my script m is the number of replicates (Wiederholungen) the script should run.
Foreach Code:
foreach(m=1:Wiederholungen)%dopar%{
A[m,,]<-m
B[m,,]<-m
C[m,,]<-m
}
Resulting in:
[[1]]
[1] 1
[[2]]
[1] 2
[[3]]
[1] 3
[[4]]
[1] 4
But this does not lead in the above result for the dataframes A,B,C. I know that foreach has a combine option but it seems only to work if you have the result for one matrix and not for several as in my example. How do I get the same result as with my old for loop using a parallel processing approach. I am using Ubuntu and 3.2.2.

Answer 1

I know this is a very old post, but thought an answer might help someone in the future.
Foreach returns a list of only the last object created in the loop. so if you want A, B, and C returned you need to list them as the final step of the loop.
This code works for me.
W<- foreach(m = 1:Wiederholungen) %dopar% {
A[m,,]<-m
B[m,,]<-m
C[m,,]<-m
list(A, B, C)
}
For future reference, the foreach vignette can be very helpful with things like this.