I tend not to use match.call for this because it feels like I'm repeating
work (argument matching) that has already been done. Also, match.call's
output needs to be processed a bit to get the expressions.
The following 2 functions give the same results, a "pairlist" of the unevaluated
arguments matching the "..." in the function definition.
f1 <- function(x, ..., atEnd) substitute(...())
f2 <- function(x, ..., atEnd) match.call(expand.dots=FALSE)$...
E.g.,
> str(f1(1, stop("don't evaluate me!"), Log=log(-10:1), atEnd=Inf))
Dotted pair list of 2
$ : language stop("don't evaluate me!")
$ Log: language log(-10:1)
> str(f2(1, stop("don't evaluate me!"), Log=log(-10:1), atEnd=Inf))
Dotted pair list of 2
$ : language stop("don't evaluate me!")
$ Log: language log(-10:1)
The former appears to be about 3 times as fast as the latter, but you need
to run it a lot of times (>10^4) to see the difference. There may be a bigger
speedup if there are lots of non-"..." arguments, but I haven't tested that.
I also use the following, which works in both S+ and R:
> f3 <- function(x, ..., atEnd) as.list(substitute(junk(...)))[-1]
> str(f3(1, stop("don't evaluate me!"), Log=log(-10:1), atEnd=Inf))
List of 2
$ : language stop("don't evaluate me!")
$ Log: language log(-10:1)
It is probably best to bury this in a utility function with an intuitive name
instead
of trying to remember the idioms. Perhaps there already is one.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: Bert Gunter [mailto:gunter.ber...@gene.com]
> Sent: Monday, July 23, 2012 2:45 PM
> To: William Dunlap
> Cc: S Ellison; Jochen Voß; r-help@r-project.org
> Subject: Re: [R] turning R expressions into functions?
>
> Bill:
>
> Is there some reason to prefer your "odd idiom" to match.call, perhaps
> as as.list(match.call()), as proposed by Hadley?
>
> -- Bert
>
> On Mon, Jul 23, 2012 at 2:25 PM, William Dunlap <wdun...@tibco.com> wrote:
> > list(...) evaluates the things in ...
> > E.g.,
> > > f0 <- function(x, ...) list(...)
> > > f0(1, warning("Hmm"), stop("Oops"), cat("some output\n"))[[2]]
> > Error in f0(1, warning("Hmm"), stop("Oops"), cat("some output\n")) : Oops
> > In addition: Warning message:
> > In f0(1, warning("Hmm"), stop("Oops"), cat("some output\n")) : Hmm
> >
> > You can use the odd idiom substitute(...()) to get the unevaluated ...
> > arguments:
> > > f1 <- function(x, ...) substitute(...())
> > > f1(1, warning("Hmm"), stop("Oops"), cat("some output\n"))
> > [[1]]
> > warning("Hmm")
> >
> > [[2]]
> > stop("Oops")
> >
> > [[3]]
> > cat("some output\n")
> >
> >
> > 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 S Ellison
> >> Sent: Monday, July 23, 2012 2:12 PM
> >> To: Jochen Voß
> >> Cc: r-help@r-project.org
> >> Subject: Re: [R] turning R expressions into functions?
> >>
> >> >> One of the things I would love to add to my package would be the
> >> >> ability to compare more than two expressions in one call. But
> >> >> unfortunately, I haven't found out so far whether (and if so, how) it
> >> >> is possible to extract the elements of a "..." object without
> >> >> evaluating them.
> >> >
> >> >Have a look at match.call.
> >>
> >> ... or use
> >> dotlist <- list(...)
> >>
> >> to get a list of everything included in ...
> >>
> >> S Ellison
> >>
> >>
> *****************************************************************
> >> **
> >> This email and any attachments are confidential. Any use...{{dropped:8}}
> >>
> >> ______________________________________________
> >> 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
>
> Internal Contact Info:
> Phone: 467-7374
> Website:
> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-
> biostatistics/pdb-ncb-home.htm
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