Great.  Thanks, Jim.

  _____  

From: jim holtman [mailto:jholtman@gmail.com] 
Sent: Sunday, December 24, 2006 1:11 AM
To: christos@nuverabio.com
Cc: r-help@lists.R-project.org
Subject: Re: [R] how to 'get' an object that is part of a list


use 'eval' and 'parse'
 

> xx
$a
[1] 1 2 3 4 5

$b
[1] "a" "b" "c" "d" "e"

> eval(parse(text='xx$a'))
[1] 1 2 3 4 5
> 


So that way you can pass in the character string and then 'parse' it.



 
On 12/24/06, Christos Hatzis <christos@nuverabio.com> wrote: 

This might be an trivial thing but I am stuck.

Consider:

xx <- list(a=1:5, b=letters[1:5]) 

Although object xx is accessible through its name,
how can object xx$b be accessed similarly through its name?

> get("xx")
$a
[1] 1 2 3 4 5

$b
[1] "a" "b" "c" "d" "e" 

> get("xx$b")
Error in get(x, envir, mode, inherits) : variable "xx$b" was not found

get("xx")$b will not work in my case because it will probably require
parsing to make it work within a function. E.g.

my.length <- function(...) {
       names <- as.character(substitute(list(...)))[-1]
       sapply(names, FUN=function(x){y <- get(x); length(y)})
}
> my.length(xx)
xx
2
> my.length (xx$a)
Error in get(x, envir, mode, inherits) : variable "xx$a" was not found
> my.length(xx$a, xx$b)
Error in get(x, envir, mode, inherits) : variable "xx$a" was not found

Thank you. 

Christos Hatzis, Ph.D.
Nuvera Biosciences, Inc.
400 West Cummings Park
Suite 5350
Woburn, MA 01801
Tel: 781-938-3830
www.nuverabio.com

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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve? 

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