How do you refer to a function's environment in R? - r

Question

I am getting the following error because I believe a clusterExport() (parallel package) I'm doing is referring to the wrong environment:
Error in get(name, envir = envir) : object 'simulatedExpReturn' not found
I am getting this in a function and specifically at the clusterExport() line of this part:
simulatedExpReturn = list()
# Calculate the number of cores
no_cores <- detectCores()
# Initiate cluster
cl <- makeCluster(no_cores)
clusterExport(cl, c("simulatedExpReturn",
"covariance",
"numAssets",
"assetNames",
"numTimePoints-lag",
"stepSize"), envir = environment(Michaud1998MonteCarlo))
covariance, numAssets, assetNames, numTimePoints-lag, and stepSize are all passed into the function. I have also tried envir = envir and envir = .GlobalEnv and neither worked.
How can this be fixed?

Answer 1

This is a scoping problem, the clusterExport function is searching for your objects in the specified environment, and exports them to each processor's child environment. It does not search the .GlobalEnv where you have defined simulatedExpReturn.
This is why the following returns 1 and not an empty list:
> Michaud1998MonteCarlo <- new.env()
> simulatedExpReturn = list()
> assign("simulatedExpReturn", 1, envir = Michaud1998MonteCarlo)
>
> # Calculate the number of cores
> no_cores <- detectCores()
>
> # Initiate cluster
> cl <- makeCluster(no_cores)
>
> clusterExport(cl, c("simulatedExpReturn"), envir = Michaud1998MonteCarlo)
> clusterCall(cl, function() simulatedExpReturn)
[[1]]
[1] 1
[[2]]
[1] 1
[[3]]
[1] 1
[[4]]
[1] 1
To resolve, simply assign the value to the environment before running the clusterExport:
assign("simulatedExpReturn", list(), envir = Michaud1998MonteCarlo)

Answer 2

A simple example of passing variable via its name to another function:
print.variable.from.env <- function (x,e) { cat("Echoing", get(x, envir = e)) }
my.f <- function()
{
my.local <- "my local "
print.variable.from.env("my.local", environment())
}
my.f()
if you run it, it will simply print
Echoing my local
i.e. by passing the environment to print.variable.from.env, the function is able to get access to the varialbe given by its name in x
And one more example:
print.variable.from.env <- function (x,e) { cat("Echoing", get(x, envir = e), "\n") }
my.f <- function()
{
my.local <- "my local "
print.variable.from.env("my.local", environment())
print.variable.from.env("global.variable", parent.env(environment()))
}
global.variable <- "global"
my.f()
This shows the access to "global.variable" from function's parent env.
When executed it'll print
Echoing my local
Echoing global

Answer 3

Or even simpler, if you just want to access the caller's environment:
print.variable.from.env <- function (x) {
cat("Echoing", get(x, envir = parent.frame()))
}
my.f <- function() {
my.local <- "my local "
print.variable.from.env("my.local")
}
my.f()