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

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Thu 05 Jan 2006 - 03:04:45 EST

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@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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