cannot open the connection error with parLapply

Question

I successfully processed some data on a 4 core computer using parLapply, using a code like below:

require(\"parallel\")
setwd(\"C:/...\")

file_summary<-read.         


        

Answer 1

The only operation that I see in "myfunction" that can generate a "cannot open the connection" error is "read.table". You might want to add the following right before calling read.table:

if (! file.exists(new_file))
  stop(paste(new_file, "does not exist"))

It might also be useful to check that the worker has permission to read the file:

if (file.access(new_file, mode=4) == -1)
  stop(paste("no read permission on", new_file))

It seems worthwhile to rule out these problems.

Answer 2

You need to pass the current directory as an argument in parLapply() to your function. Inside your function myfunction you need to reset the working directory by setwd():

myfunction = function(k, wd_)
{
      setwd(wd_)
        ...
}
...
wd_ = getwd()
Results <- parLapply(Cl, c(1:n_tasks), myfunction, wd_)

N.B. make sure R/R Studio/R Script all are not blocked by the firewall.