Re: [R] How to share variables

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Tue 22 Aug 2006 - 22:32:09 EST

On 8/22/06, Sergio Martino <s.martino@tno.it> wrote:
> Hi
>
> Thanks again. I hope not to waste to much of your time.
>
> I delete some lines of your answer
>
> > Each time myfun is run a new environment is created to hold
> > its local variables. The parent of that environment is e in
> > this example by construction. So e and the environment that
> > is temporarily created to hold myfun's variables are distinct.
>
> This means that the enviroment is duplicated, ie it is present twince in
> memory?

Each time myfun starts up a new environment comes into being that contains x and each time it completes that environment is destroyed.

> I must keep some big variables and it will be a waste of memory; moreover if
> I update a value it will be lost.

If you update a local variable then its lost upon exit (of course you could return the variable or return the environment inside the function) but if you update it in e then its not lost.

>
> > > If I can use inside myfun the variable as e$dat (without changing the
> > > enviroment (no environment(myfun) <- e statement)) than it will be ok.
> >
> > Yes you can. You can either make sure that e is visible to myfun
> > via normal scoping rules or pass it explicitly:
> >
> > e <- new.env()
> > e$dat <- 1:3
> > myfun <- function(x) sum(x + e$dat)
> > myfun(10)
> >
>
> Hit!!!
> It solves the problem.
> A small drawback is that I need to modify the name of each occurrence of the
> variable.

That's why in an earlier example we set the environment of myfun to e.

>
>
> > # or passing e explicitly
> >
> > myfun2 <- function(x, e) sum(x + e$dat)
> > myfun2(10, e)
> >
>
> Any overhead in passing the environment? Is it a pointer?

?system.time

to experiment with timings.

>
> Sergio
>
>



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