r - Using source() within parallel foreach loops

Question

Here is a toy example to illustrate my problem.

library(foreach)
library(doMC)
registerDoMC(cores=2)

foreach(i = 1:2) %dopar%{
  i + 2
}
[[1]]
[1] 3

[[2]]
[1] 4

So far so good...

But if the code i + 2 is saved in the file addition.R and that I call that file using source() then

> foreach(i = 1:2) %dopar%{
+   source("addition.R")
+ }
Error in { : task 1 failed - "object 'i' not found"

Answer 1

I cannot fully reproduce your toy, but I had a smiliar problem, which I was able to solve by:

source(file, local = TRUE)

which should parse the source in the local environment, i.e. recognizing i.