[R] Putting an object in to a function that calls the current function

[Gabor Grothendieck]

Try

   demo(scoping)

which shows a situation similar to the one Duncan describes
but uses several functions.

On 1/4/06, Ales Ziberna <aleszib2 at gmail.com> wrote:
> I do not belive this would work in my case, since as I said, the function is
> called by several different functions.
>
> Ales Ziberna
>
> -----Original Message-----
> From: Duncan Murdoch [mailto:murdoch at stats.uwo.ca]
> Sent: Wednesday, January 04, 2006 5:05 PM
> To: Ales Ziberna
> Cc: 'R-help'
> Subject: Re: [R] Putting an object in to a function that calls the current
> function
>
> On 1/4/2006 10:32 AM, Ales Ziberna wrote:
> > Thank you both (Duncan Murdoch and  Gabor Grotehendieck) for your answers.
> > Both work and my problem is solved.
> >
> > I do aggree with Duncan Murdoch that usually messing with the
> > environment of your caller is a bad idea. The reason why I still want
> > to do it in this case is that I exactly know which functions are
> > calling (the function is NEVER called directly) it and it was in this
> > case easier to use this than to modify each of the fuctions that are
> calling it.
>
> Using R's lexical scope may lead to a cleaner solution.  That is, you define
> the functions within the one that calls them; then a <<- "ok"
> would do what you want (provided "a" existed in the enclosure at the time).
>
> For example,
>
> f <- function() {
>        a <- "init"
>        s <- function() {
>                a <<- "ok"
>         }
>        s()
>        print(a)
> }
>
> Duncan Murdoch
>
> >
> > Thanks again!
> > Ales Ziberna
> >
> > -----Original Message-----
> > From: Duncan Murdoch [mailto:murdoch at stats.uwo.ca]
> > Sent: Wednesday, January 04, 2006 3:26 PM
> > To: Ales Ziberna
> > Cc: R-help
> > Subject: Re: [R] Putting an object in to a function that calls the
> > current function
> >
> > On 1/4/2006 9:14 AM, Ales Ziberna wrote:
> >> Hello!
> >>
> >> I would like to put an object in to a function that calls the current
> >> function.
> >>
> >> I thought the answer will be clear to me after reading the help files:
> >> ?assign
> >> ?sys.parent
> >>
> >> However it is not.
> >> Here is an example I thought should work, however it dose not exactly:
> >>
> >> f<-function(){s();print(a)}
> >> s<-function()assign(x="a",value="ok",pos=sys.parent())
> >> f() #I want to get "ok"
> >> a #I do not want "a" in global enviorment, so here I should get
> >> #Error: Object "a" not found
> >> ff<-function()f() #here I also want to get "ok" - it should not
> >> matter if the parent fuction has any parents
> >>
> >> Thank you in advance for suggestions!
> >
> > That's not a good idea.  Why would you want to do something like that?
> >
> > That out of the way, here's a function that does it:
> >
> > f<-function(){s();print(a)}
> > s<-function()assign(x="a",value="ok",env=parent.frame())
> >
> > The difference between pos=sys.parent() and env=parent.frame() is that
> > the pos is interpreted as a position in the search list (see ?assign),
> > while
> > parent.frame() gives you the environment from the stack, equivalent to
> > sys.frame(sys.parent()).
> >
> > In R you're almost certainly better off working directly with
> > environments, rather than going through integer indexing the way you
> > (used to?) have to do in S-PLUS.
> >
> > Did I mention that messing with the environment of your caller is a
> > bad idea?  It's not yours, don't touch it.
> >
> > Duncan Murdoch
>
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