R help - Nov 2012 - Extracting list names within a looped function

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?

Any help would be greatly appreciated!

Many thanks,

  -- Stan

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