[R] What is the most efficient way to assign to PARTS of obje cts in other frames/environments?

[Raubertas, Richard]

For nested function calls it appears that a combination of environment()
and '<<-' will also work:

f1 <- function() {
  x <- rep(NA,4)                   # Object to be modified by function f2
  environment(f2) <- sys.frame(1)  # Make f1's environment available to f2
  f2(2)                            # Changes 2nd element of x
  print(x)
}

f2 <- function(i) {
  # Following works because "<<-" searches through all available
  # environments for the LHS symbol, and does assignment where the
  # symbol is found.  "x" is in the environment of f1, which was 
  # made available to f2 above.
  x[i] <<- i^2
  NULL
}

f1()  # prints NA 4 NA NA

Of course this requires that f1 anticipate that f2 will want to 
modify its objects; i.e., f1 and f2 must be written as a pair, to 
know about each other.

Richard Raubertas
Biometrics Research
Merck & Co.

> -----Original Message-----
> From: Thomas Lumley [mailto:tlumley at u.washington.edu]
> Sent: Friday, May 17, 2002 11:44 AM
> To: oehl_list at gmx.de
> Cc: r-help at stat.math.ethz.ch; Martin.Schlather at uni-bayreuth.de
> Subject: Re: [R] What is the most efficient way to assign to PARTS of
> objects in other frames/environments?
> 
> 
> On Fri, 17 May 2002 oehl_list at gmx.de wrote:
> 
> > Can please someone familiar with the R internals explain on 
> the following:
> >
> > PR#1434 from r-bugs clarifies that
> >
> >   assign("a[1]", x, SomeOtherFrame)
> >
> > or
> >
> >   assign("a$a", x, SomeOtherFrame)
> >
> > will NOT assign to an object 'a' in the other frame BUT 
> create a new object
> > called 'a[1]' resp. 'a$a'.
> >
> > This leads to the following question: what is the most 
> efficient way to
> > assign to PARTS of objects in other frames/environments?
> >
> > Any way I know appears to have some problems associated:
> >
> > # doing it locally involves several calls and probably 
> copies the whole
> > object
> > local.copy <- get("a", SomeOtherFrame)
> > local.copy$a <- x
> > assign("a", local.copy, SomeOtherFrame)
> >
> > # using eval fails because x might be unknown in the other frame
> > > t1 <- function(){
> > +   # x is locally defined
> > +   x <- 9
> > +   eval(parse(text="a$a <- x"), envir=globalenv())
> > + }
> > > t1()
> > Error in eval(expr, envir, enclos) : Object "x" not found
> >
> 
> Instead of
> 
>   assign("a$a",x,envir=SomeOtherFrame)
> you can do
>   eval(substitute(a$a<-localx,localx=x),envir=SomeOtherFrame)
> 
> 
> 	-thomas
> 
> Thomas Lumley			Asst. Professor, Biostatistics
> tlumley at u.washington.edu	University of Washington, Seattle
> 
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