[R] how to 'get' an object that is part of a list

[Duncan Murdoch]

On 12/24/2006 12:06 AM, Christos Hatzis 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?

name <- "b"
xx[[name]]

will work.

Duncan Murdoch

>  
>> 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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