I think Bert Gunter is right, but do you want partial matches (not found by
match), and how robust do you want the code to be?
f <- function(…)
{ pos <- match('a', ...names())
if (is.na(pos))
stop("a is required.")
…elt(pos)
}
Incidentally, what is the best way to extract the expression without evaluating
it?
g <- function(...)
{ pos <- match('a',...names())
if (is.na(pos))
stop("a is missing.")
(function(a,...) substitute(a)) (...)
}
Regards,
Jorgen Harmse.
Message: 8
Date: Sun, 5 Jan 2025 11:17:02 -0800
From: Bert Gunter <bgunter.4...@gmail.com>
To: Iris Simmons <ikwsi...@gmail.com>
Cc: R-help <R-help@r-project.org>
Subject: Re: [R] Extracting specific arguments from "..."
Message-ID:
<cagxfjbronopt-bodf6srpp79bwucppoo3+ycdgn3y-ytdu5...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Thanks, Iris.
That is what I suspected, but it wasn't clear to me from the docs.
Best,
Bert
On Sun, Jan 5, 2025 at 10:16 AM Iris Simmons <ikwsi...@gmail.com> wrote:
>
> I would use two because it does not force the evaluation of the other
> arguments in the ... list.
>
>
>
> On Sun, Jan 5, 2025, 13:00 Bert Gunter <bgunter.4...@gmail.com> wrote:
>>
>> Consider:
>>
>> f1 <- function(...){
>> one <- list(...)[['a']]
>> two <- ...elt(match('a', ...names()))
>> c(one, two)
>> }
>> ## Here "..." is an argument list with "a" somewhere in it, but in an
>> unknown position.
>>
>> > f1(b=5, a = 2, c=7)
>> [1] 2 2
>>
>> Which is better for extracting a specific named argument, one<- or
>> two<- ? Or a third alternative that is better than both?
>> Comments and critiques welcome.
>>
>> Cheers,
>> Bert
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.
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