On Oct 19, 2013, at 19:03 , Duncan Murdoch wrote:
> On 13-10-18 1:54 PM, Bert Gunter wrote:
>> 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 suspect it's a bug, though I can't see it's one that's likely to need
> fixing. The general idea is that a function call like ...() is parsed into a
> pairlist containing just the name "...", then substitute replaces it with the
> content of that variable, which is a pairlist containing the unevaluated
> argument list. So by that analysis, you might expect to get the same result
> using
>
> pairlist(...)
>
> However, you don't, because the latter expression evaluates all the arguments
> to the function, while Bill's idiom leaves them unevaluated. I can't think of
> any documented reason why that should be, but on the other hand, I can't
> think of any reason it would cause problems. So I'd say it's unlikely to be
> deliberately changed, but it might change as a result of some internal change
> to R.
>
> Duncan Murdoch
>
Just curious, does substitute(...()) buy you anything that you don't get from
the straightforward
match.call(expand.dots=FALSE)$...
???
-pd
>
>>
>> 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 <wdun...@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-boun...@r-project.org [mailto:r-help-boun...@r-project.org]
>>>> On Behalf
>>>> Of Dan Abner
>>>> Sent: Friday, October 18, 2013 9:06 AM
>>>> To: r-help@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@r-project.org mailing list
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>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>> ______________________________________________
>>> R-help@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@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.
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd....@cbs.dk Priv: pda...@gmail.com
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