Question

I am trying to run code on several cores (I tried both the snow and parallel packages). I have

cl <- makeCluster(2)
y  <- 1:10
sapply(1:5, function(x) x + y)  # Works
parSapply(cl, 1:5, function(x) x + y)

The last line returns the error:

Error in checkForRemoteErrors(val) : 
  2 nodes produced errors; first error: object 'y' not found

Clearly parSapply isn’t finding y in the global environment. Any ways to get around this? Thanks.

Answer 1

The nodes don’t know about the y in the global environment on the master. You need to tell them somehow.

library(parallel)
cl <- makeCluster(2)
y  <- 1:10
# add y to function definition and parSapply call
parSapply(cl, 1:5, function(x,y) x + y, y)
# export y to the global environment of each node
# then call your original code
clusterExport(cl, "y")
parSapply(cl, 1:5, function(x) x + y)