Using global variable in function

Question

I have a very big dataset and I analyze it with R.

The problem is that I want to add some columns with different treatments on my dataset AND I need some recursive function which use some global variable. Each function modify some global variable et create some variables. So the duplication of my dataset in memory is a big problem...

I read some documentation: if I didn't misunderstand, neither the use of <<- nor assign() could help me...

What I want:

mydata <- list(read.table(), ...)
myfunction <- function(var1, var2) {
   #modification of global mydata
   mydata = ...
   #definition of another variable with the new mydata
   var3 <- ...
   #recursive function
   mydata = myfunction(var2, var3)
}

Do you have some suggestions for my problem?

Konrad Rudolph · Accepted Answer · 2015-09-24 12:18:44Z

5

Both <<- and assign will work:

myfunction <- function(var1, var2) {
   # Modification of global mydata
   mydata <<- ...
   # Alternatively:
   #assign('mydata', ..., globalenv())

   # Assign locally as well
   mydata <- mydata

   # Definition of another variable with the new mydata
   var3 <- ...

   # Recursive function
   mydata = myfunction(var2, var3)
}

That said, it’s almost always a bad idea to want to modify global data from a function, and there’s almost certainly a more elegant solution to this.

Furthermore, note that <<- is actually not the same as assigning to a variable in globalenv(), rather, it assigns to a variable in the parent scope, whatever that may be. For functions defined in the global environment, it’s the global environment. For functions defined elsewhere, it’s not the global environment.

edited Sep 24, 2015 at 12:18

answered Sep 24, 2015 at 11:10

Konrad Rudolph

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3 Comments

EaudeRoche Over a year ago

I knew that, but when I coded it: assign() or <<- I modified mydata in the global environment but not in the local environment of my function. So when I used the recursive function in myfunction() : the modifications were not apply. The modifications are like : dataset[dataset[, "colx"]==var1, ] = anotherfunction() so assign() is not really handy here for me...

Konrad Rudolph Over a year ago

@EaudeRoche Oh, got it. But actually the solution to this is straightforward: do two assigns, one local and one nonlocal. See my edit. You can also change the order of these operations around: assign first locally and then globally.

EaudeRoche Over a year ago

@konrad-rudolf OK ! So I will have to duplicate the dataset for each iteration anyway.

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