Assign function output with assign

Question

I am using

library(foreach)
library(doSNOW)

And I have a function mystoploss(data,n=14)

I then call it like that (I want to loop over n=14 for now):

registerDoSNOW(makeCluster(4, type = "SOCK"))

foreach(i = 14) %dopar% {assign(paste("Performance",i,sep=""),
mystoploss(data=mydata,n=i))}

I then try to find Performance14 from above, but it is not assigned.

Is there some way to assign so the output will be in Performance14?

And if I use

foreach(i = 14) %dopar% {assign(paste("Performance",i,sep=""),
    mystoploss(data=mydata,n=i),envir = .GlobalEnv)}

I get error :

Error in e$fun(obj, substitute(ex), parent.frame(), e$data) : 
  worker initialization failed: Error in as.name

Best Regards

Community · Accepted Answer · 2017-05-23 11:57:45Z

1

This is because the assign operations are happening in the worker processes. The vaues of the variables are being sent back (see your R session console) but not with the names you assigned. You need to capture these values and assign them names again. See this related question.

The following is an alternative that may be of help: asign the output of foreach to an intermediate variable and assign it to your desired variables in the current 'master process' environment.

PerformanceAll <- foreach(i = 1:14,.combine="c") %dopar% { mystoploss(data=mydata,n=i) } #pick .combine appropriately
for(i in 1:14){ assign(paste("Performance",i,sep=""), PerformanceAll[i]) }

Here is the full example I tried:

library(foreach)
library(doSNOW)
mystoploss <- function(data=1,n=1){
  return(runif(data)) #some operation, returns a scalar
}
mydata <- 1
registerDoSNOW(makeCluster(4, type = "SOCK"))
PerformanceAll <- foreach(i = 1:14,.combine="c") %dopar% { mystoploss(data=mydata,n=i) }#pick .combine appropriately
for(i in 1:14){ assign(paste("Performance",i,sep=""), PerformanceAll[i]) }

Edit: If the output of mystoploss is a list, then do the following changes:

mystoploss <- function(data=1,n=1){#Example
  return(list(a=runif(data),b=1)) #some operation, return a list
}
PerformanceAll <- foreach(i = 1:14) %dopar% { mystoploss(data=mydata,n=i) }#remove .combine
for(i in 1:14){ assign(paste("Performance",i,sep=""), PerformanceAll[[i]]) } #double brackets

edited May 23, 2017 at 11:57

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answered Jul 24, 2014 at 12:12

Theja Tulabandhula

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3 Comments

user1665355 Over a year ago

Ok! My function returns a list so I would like to combine my results so the output is a nested list.

Theja Tulabandhula Over a year ago

In that case, leave the .combine option out (the default behaviour here is that foreach %dopar% returns a list for each value of i). PerformanceAll will be a list of lists.

user1665355 Over a year ago

Great! Did not know that I could assign directly to an object with foreach, PerformanceAll <- foreach(..., like I mean you can't assign like that with a for-loop. Thanks for the help!

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