[R] How to output name of object

[Prof Brian Ripley]

On 18/06/2014 15:01, Bert Gunter wrote:
> Would
>
> f <- function (...)
> {
>    sapply(substitute(list(...)),deparse)[-1]
> }
>
>> f(a1=log(1:4), m1=1:4, c1=pi)
>          a1         m1         c1
> "log(1:4)"      "1:4"       "pi"
>
> be equivalent?
> I find the substitute(...()) construction completely mysterious, while
> substitute(list(...)) makes sense to me.

It would give the same result.  If starting from scratch I would 
probably have used

f <- function(...) as.character(match.call()[-1])

but that does not give names (if wanted) whereas

f <- function(...) sapply(match.call(), deparse)[-1]

does


My main point was that a for() loop (and extending a logical vector 
initialized to NA and then coerced to character) seems rather unnatural. 
  And seq_along would be clearer if you really must use a loop.

>
> Cheers,
> Bert
>
>
>
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
> (650) 467-7374
>
> "Data is not information. Information is not knowledge. And knowledge
> is certainly not wisdom."
> Clifford Stoll
>
>
>
>
> On Wed, Jun 18, 2014 at 5:41 AM, Prof Brian Ripley
> <ripley at stats.ox.ac.uk> wrote:
>> On 18/06/2014 12:54, Jim Lemon wrote:
>>>
>>> On Wed, 18 Jun 2014 04:24:58 PM yzh lin wrote:
>>>>
>>>> Hi, every R user,
>>>>
>>>>      I wanna output  names of objects, I googled codes from website,
>>>
>>> but it
>>>>
>>>> was not what I wanted.
>>>>
>>>> the codes are as following:
>>>>
>>>> f <- function (...)
>>>> {
>>>>     unevaluatedArgs <- substitute(...())
>>>>     evaluatedArgs <- list(...)
>>>>     stopifnot(length(unevaluatedArgs) == length(evaluatedArgs))
>>>>     tags <- vapply(unevaluatedArgs, FUN=function(x) deparse(x)[1],
>>>>                    FUN.VALUE=character(1))
>>>>     if (!is.null(tmp <- names(evaluatedArgs))) {
>>>>       # if argument is tagged, tag=expr, use the tag
>>>>       i <- !is.na(tmp) & tmp != ""
>>>>       tags[i] <- tmp[i]
>>>>     }
>>>>     tags
>>>> }
>>>>
>>>> f(a1=log(1:4), m1=1:4, c1=pi)
>>>>
>>>> results:
>>>>>
>>>>> f(a1=log(1:4), m1=1:4, c1=pi)
>>>>
>>>>
>>>>     a1   m1   c1
>>>> "a1" "m1" "c1"
>>>>
>>>>
>>>> what I wanted is outputting "log(1:4) " "1:4", "pi" , while not "a1" "m1"
>>>> "c1" .
>>>>
>>>> Coulde someone tell me how to get the results I wanted?
>>>>
>>> Hi Yuanzhen,
>>> This may be of some help:
>>>
>>> f<-function (...) {
>>>     unevaluatedArgs <- unlist(substitute(...()))
>>>     tags<-NA
>>>     for(arg in 1:length(unevaluatedArgs))
>>>      tags[arg]<-deparse(unevaluatedArgs[[arg]])
>>>     tags
>>> }
>>>
>>> f(a1=log(1:4), m1=1:4, c1=pi)
>>> [1] "log(1:4)" "1:4"      "pi"
>>
>>
>> Or simply
>>
>> f <- function(...) sapply(subsitute(...()), deparse)
>>
>> which even keeps the names.
>>
>> --
>> Brian D. Ripley,                  ripley at stats.ox.ac.uk
>> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
>> University of Oxford,             Tel:  +44 1865 272861 (self)
>> 1 South Parks Road,                     +44 1865 272866 (PA)
>> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595