You have to understand the difference between the lexical scope of a
function (which gives the search path for variables) and call stack (which
is a path of function calls). This gives an enormous flexibility in
programming, perhaps at the cost of confusing some people.
See http://cran.r-project.org/doc/manuals/R-intro.html#Scope
http://cran.r-project.org/doc/manuals/R-lang.html#Scope
and
http://cran.r-project.org/doc/manuals/R-lang.html#Scope-of-variables
Here is a slightly corrected Steve's example:
f1 <- function(name, envir=parent.frame()){
#`name` is a string here, objects are referenced by their names in R and
not pointers
assign(name, 1, envir=envir)
#assignment is made in the parent.environment which is an environment
of calling function
}
f2 <- function(n){
i <- n
f1("i") #pass the name of an object and not an object as you did in
your original example
print(i)
}
Now,
i <- 10
f1("i")
i
[1] 1
f2(2323)
[1] 1 #not 2323
On Fri, 07 Aug 2009 00:02:35 +0200, Ivo Shterev <idc...@yahoo.com> wrote:
Hi,
Perhaps I have to rephrase a bit my question. If we have the following:
i = 10
f1 = function(i){
i <<- 1
}
after calling f1, the value of i becomes 1. Now, suppose that f1 is
called in another function f2, and i is initialized in f2 as well, i.e:
f2 = function(n){
i = n
f1(i)
}
The intention is, after executing f2, i=1 (not i=n).
--- On Thu, 8/6/09, Steve Lianoglou <mailinglist.honey...@gmail.com>
wrote:
From: Steve Lianoglou <mailinglist.honey...@gmail.com>
Subject: Re: [R] A question regarding R scoping
To: "Ivo Shterev" <idc...@yahoo.com>
Cc: r-help@r-project.org
Date: Thursday, August 6, 2009, 10:23 PM
Howdy,
On Aug 6, 2009, at 4:11 PM, Ivo Shterev wrote:
> Hi,
>
> The intention is that after executing f2, the value of
i to become 1.
>
> f1 = function(i){i = 1}
>
> f2 = function(n){ i = length(n)
> f1(i)
> print(i)}
>
> i.e. f2 should print 1, not length(n).
Yeah, you can using parent.frame()'s and such:
f1 <- function(i) assign('i', 10, envir=parent.frame())
f2 <- function(n) {
i <- length(n)
f1(i)
print(i)
}
R> f2(1:20)
[1] 10
Honestly, this just smells like a *really* bad idea, though
... just have f1() return a value that you use in f2.
-steve
--
Steve Lianoglou
Graduate Student: Computational Systems Biology
| Memorial Sloan-Kettering Cancer Center
| Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
