[R] Extracting list names within a looped function

Berend Hasselman
Thu, 15 Nov 2012 10:27:00 -0000

On 15-11-2012, at 11:14, Gaj Stan (BIGCAT) wrote:

> Hello all,
>
> I have the following problem:
>
> 1) A list was defined as 'a'
>
> a <- list("var1"=c(100:1), "var2"=c(1:100),
"var3"=rnorm(100))
>
> 2) a function 'foo' was defined that extracts the variable name
assigned to x using the deparse(substitute()) functionality. This name will then
be used within the function to generate specific output files, etc.
>
> foo <- function(x) {
>  print( deparse(substitute(x)) )
> }
>
> However, I am currently interested in looping through all list variables
and extract the list variable name from within the function. The current loop
(see below) will result in
>
> for(i in 1:length(a)) {
>  foo(a[[i]])
> }
> [1] "a[[i]]"
>
> which actually does what I expected of deparse(substitute(x)), but is not
what I wanted. I would like to end up with something like
>
> [1] "var1"
> [1] "var2"
> [1] "var3"
>
> or
>
> [1] "a[[\"var1\"]]"
> [1] "a[[\"var2\"]]"
> [1] "a[[\"var3\"]]"
>
> Keep in mind that x has to be a matrix, and not a list. This to keep the
function as general as possible.
>
> Does anyone have any idea on how to tackle this? Is deparse(substitute(x))
here the best way to go? Are there alternatives?

I'm not sure if I understand what you want but will this give you what you
seem to want:

names(a)

Berend