Question

I want to initialize libraries in cluster by their names represented as strings.

This code works fine:

library(snowfall, rlecuyer, rsprng)
sfInit(parallel = TRUE, cpus = 4, type = "SOCK")
sfClusterEval(library(e1071))

And this code produces en error: 4 nodes produced errors; first error: object 'expr' not found

library(snowfall, rlecuyer, rsprng)
sfInit(parallel = TRUE, cpus = 4, type = "SOCK")
lib <- "e1071"
expr <- parse(text=paste("library(", lib, ")", sep=""))
sfClusterEval(expr)

So sfClusterEval try to evaluate expr and not an expression which expr contains. I cannot undestand which type of expression should be passed to sfClusterEval function, which uses substitute in its body

> sfClusterEval
function (expr, stopOnError = TRUE) 
{
    sfCheck()
    if (sfParallel()) {
        return(sfClusterCall(eval, substitute(expr), env = globalenv(), 
            stopOnError = stopOnError))
    }
    else {
        return(eval(expr, envir = globalenv(), enclos = parent.frame()))
    }
}

This question seems simple, but I could not solve it and need someone’s advice.

UPDATE:

Further investigation details on simplier examples. I feel that the truth is near.
This code works fine

sfClusterEval(library("e1071"))

But this call produces en error: 4 nodes produced errors; first error: object ‘lib’ not found

lib <- "e1071"
sfClusterEval(library(lib, character.only=TRUE))

ANSWER:

The variable lib should be exported to the cluster previously. And after that it can be removed.

lib <- "e1071"
sfExport("lib")
sfClusterEval(library(lib, character.only=TRUE))
sfRemove("lib")

Thanks for Richie, for giving the starting idea!

Answer 1

You can use sfLibrary to load extra packages on workers. See ?snowfall and click snowfall-tools.