At 19:05 18/10/2013, William Dunlap wrote:
> 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
Well it brightened up my day. Not sure whether that is sufficient or
necessary for it to be a fortune.
> -----Original Message-----
> From: Bert Gunter [mailto:gunter.ber...@gene.com]
> Sent: Friday, October 18, 2013 10:54 AM
> To: William Dunlap
> Cc: Dan Abner; r-help@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 <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
> >> 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.
>
>
>
> --
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
>
> (650) 467-7374
Michael Dewey
i...@aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html
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