[R] Fortune?, was Re: Recovering object names when using the ... argument in a fn XXXX

[Michael Dewey]

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.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

Michael Dewey
info at aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html