[Rd] length of `...`

[Gabe Becker]

As of 3.5.0 the ...length() function does exactly what you are asking for.
Before that, I don't know of an easy way to get the length without
evaluation via R code. There may be one I'm not thinking of though, I
haven't needed to do this myself.

Hope that helps.

~G

On Thu, May 3, 2018 at 7:52 AM, Mark van der Loo <mark.vanderloo at gmail.com>
wrote:

> This question is better aimed at the r-help mailinglist as it is not about
> developing R itself.
>
>
> having said that,
>
> I can only gues why you want to do this, but why not do something like
> this:
>
>
> f <- function(...){
>    L <- list(...)
>    len <- length()
>   # you can stll pass the ... as follows:
>   do.call(someotherfunction, L)
>
> }
>
>
> -Mark
>
> Op do 3 mei 2018 om 16:29 schreef Dénes Tóth <toth.denes at kogentum.hu>:
>
> > Hi,
> >
> >
> > In some cases the number of arguments passed as ... must be determined
> > inside a function, without evaluating the arguments themselves. I use
> > the following construct:
> >
> > dotlength <- function(...) length(substitute(expression(...))) - 1L
> >
> > # Usage (returns 3):
> > dotlength(1, 4, something = undefined)
> >
> > How can I define a method for length() which could be called directly on
> > `...`? Or is it an intention to extend the base length() function to
> > accept ellipses?
> >
> >
> > Regards,
> > Denes
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
>
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>



-- 
Gabriel Becker, Ph.D
Scientist
Bioinformatics and Computational Biology
Genentech Research

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