[R] Recovering object names when using the ... argument in a fn XXXX

[Bert Gunter]

Yes, similar, but better, as match.call() will get unwanted named
arguments, too.

However, I do not understand the

substitute(...())

idiom. Would you care to explain it? (No is an acceptable  answer!).

I would have expressed it as:

as.list(substitute(list(...)))[-1]

to convert the parse tree to a list. (which is again better than using
match.call() ).

Best,
Bert

On Fri, Oct 18, 2013 at 10:27 AM, William Dunlap <wdunlap at tibco.com> wrote:
>> I am using the ... argument to parmeterize a user define fn to accept
>> multiple input objects. I subsquently save all these data as a list.
>> Question: what is the best way to recover or extract the original object
>> names that were fed to the fn?
>
> The following function, ellipsisInfo, returns character strings representing the
> actual arguments to the function.  If the function was called with tags on the
> arguments, as in ellipsisInfo(tag=argument), it makes those tags the names
> on the returned character  vector.  It does not evaluate the ... arguments, so
> you don't run into problems with evaluating arguments too soon or evaluating
> ones that should not be evaluated most of the time.
>
> ellipsisInfo <- function(...) {
>     # get the unevaluated expressions given as arguments
>     unevaluatedArgs <- substitute(...())
>     # convert those expressions to text (truncate to single line)
>     unevaluatedArgsAsText <- vapply(unevaluatedArgs, function(a)deparse(a)[1], "")
>     unevaluatedArgsAsText
> }
>
> E.g.,
>
>> i <- ellipsisInfo(x, log(10), e=exp(1), onProblem=stop("there was a problem"))
>> i
>
>                             "x"
>
>                       "log(10)"
>                               e
>                        "exp(1)"
>                       onProblem
> "stop(\"there was a problem\")"
>> ifelse(names(i)=="", i, names(i)) # use tag if supplied, otherwise argument itself
> [1] "x"         "log(10)"   "e"
> [4] "onProblem"
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
>> Of Dan Abner
>> Sent: Friday, October 18, 2013 9:06 AM
>> To: r-help at r-project.org
>> Subject: [R] Recovering object names when using the ... argument in a fn XXXX
>>
>> Hi all,
>>
>> I am using the ... argument to parmeterize a user define fn to accept
>> multiple input objects. I subsquently save all these data as a list.
>> Question: what is the best way to recover or extract the original object
>> names that were fed to the fn?
>>
>> Thanks,
>>
>> Dan
>>
>>       [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

(650) 467-7374