R - problem with foreach %dopar% inside function called by optim

Question

Calling a function that includes foreach %dopar% construct from optim causes an error:

> workers <- startWorkers(6) # 6 cores
> 
> registerDoSMP(         


        

Answer 1

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

install.packages("doSNOW")

install.packages("doParallel") 

install.packages("doMPI")

As mentioned in various threads at StackOverflow, these are responsible for parallelism in R. Bug which existed in old versions of these packages is now removed. It worked in my case. I should mention that it will most likely help even though you are not using these packages in your project/package.