R help - May 2002 - What is the most efficient way to assign to PARTS of objects in other frames/environments?

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


For me, it would highly make sense, if assign("a[1]") WOULD parse
"a[1]" and
assign to a's part, as Martin expected it to do. The same applies to
get("a[1]", SomeOtherFrame). 

BTW: this issue dates back to 1997, when I tried (for S+Version3) to
implement a library "ref" that allows to access objects in other
frames via
"references".

I would appreciate any clarification on this one.

Best


Jens Oehlschl?gel


-- 



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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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