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

[William Dunlap]

> However, I do not understand the
>    substitute(...())
> idiom. Would you care to explain it? (No is an acceptable  answer!).

I don't completely understand it either, I treat it as an idiom.  I saw it on this list once.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: Bert Gunter [mailto:gunter.berton at gene.com]
> Sent: Friday, October 18, 2013 10:54 AM
> To: William Dunlap
> Cc: Dan Abner; r-help at r-project.org
> Subject: Re: [R] Recovering object names when using the ... argument in a fn XXXX
> 
> 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