Parallel execution of train in caret fails with function not found
The error that you're getting is caused by a bug in caret 6.0-21 when using doParallel, doSNOW, and doMPI. It's been fixed in version 6.0-22 in R-forge, but hasn't been released to CRAN yet. If you don't want to wait for the new version to be released, you can:
- Downgrade to caret 5.x
- Install caret 6.0-22 from R-forge
- Install and use doSNOW 1.0.10 from R-forge rather than doParallel
The problem was caused by a change in CRAN policy that forbids the use of the ::: operator, even when referencing non-exported functions from within the same package.
Update
Caret 6.0-22 was released to CRAN on 2014-01-18. This should resolve the reported problem using caret with doSNOW and similar parallel backends.