[R] Names of objects passed as ... to a function?

[Gavin Simpson]

On Sat, 2007-06-23 at 16:52 +0100, Prof Brian Ripley wrote:
> On Sat, 23 Jun 2007, Gavin Simpson wrote:
> 
> > Dear list,
> >
> > I have a function whose first argument is '...'. Each element of '...'
> > is a data frame, and there will be at least 2 data frames in '...'. The
> > function processes each of the data frames in '...' and returns a list,
> > whose components are the processed data frames. I would like to name the
> > components of this returned list with the names of the original data
> > frames.
> >
> > Normally I'd use deparse(substitute()) to do this, but here I do not
> > know the appropriate argument to run deparse(substitute()) on, and doing
> > this on ... only returns a single "name":
> >
> >> foo <- function(...)
> > +                 deparse(substitute(...))
> >> dat1 <- rnorm(10)
> >> dat2 <- runif(10)
> >> foo(dat1, dat2)
> > [1] "dat1"
> >
> > Can anyone suggest to me a way to get the names of objects passed as
> > the ... argument of a function?
> 
> That's a little tricky.  The following may suffice:
> 
> foo <- function(...)
> {
>    as.character(match.call())[-1]
> }

Thanks Brian and Marc for this solution. I simplified my example too
much, as in reality there are additional arguments after '...', but with
a minor change to the solution you provided I got it working.

> 
> The problem is that under certain circumstances match.call can give names 
> like '..2'
> 
> > bar <- function(...) foo(...)
> > bar(dat1, dat2)
> [1] "..1" "..2"
> 
> and I don't know a comprehensive R-level solution to that.

Are there any particular situations (other than the one you show) that
you are aware of when this might happen? I will put a Warning section in
the Rd page for my function explaining that it might not name the
components correctly, so any further examples of where this might not
work could be helpful in writing that.

All the best,

G
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Gavin Simpson                     [t] +44 (0)20 7679 0522
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