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

[Duncan Murdoch]

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