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

From: Ales Ziberna <aleszib_at_gmail.com>
Date: Thu 05 Jan 2006 - 02:32:01 EST


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.

Thanks again!
Ales Ziberna

-----Original Message-----
From: Duncan Murdoch [mailto:murdoch@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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