R help - Mar 2012 - no partial matching of argument names after dots argument - why?

I noticed that the argument names after the dots argument are not partially
matched.

foo <- function(one, two, ...){
  one + two
}
> foo(o=1, t=2)
[1] 3

foo <- function(one, ..., two){
   one + two
}   
> foo(o=1, t=2) 
Fehler in one + two : 'two' fehlt


Can someone explain me the reason for this behavior?

THX
Mark 

????????????????????????????????????
Mark Heckmann
Blog: www.markheckmann.de
R-Blog: http://ryouready.wordpress.com

On 05/03/2012 09:24, Mark Heckmann wrote:
> I noticed that the argument names after the dots argument are not partially
matched.
>
> foo<- function(one, two, ...){
>    one + two
> }
>> foo(o=1, t=2)
> [1] 3
>
> foo<- function(one, ..., two){
>     one + two
> }
>
>> foo(o=1, t=2)
> Fehler in one + two : 'two' fehlt
>
>
> Can someone explain me the reason for this behavior?
It is documented in the 'R Language Definition', Venables & Ripley
'S
Programming' and perhaps elsewhere.  It is a useful feature that is not 
used often enough.

Reason: how else could you pass an argument 't' through ... ?  People do
get caught by this with things like lapply(fn, X=X), so where ... is 
involved it is always best to name exactly all arguments.  (It is more 
efficient and easier to read if you do it anyway, which is why R CMD 
check nowadays NOTEs any uses of partial matching in a package it is 
testing.)
> THX
> Mark
>
> ????????????????????????????????????
> Mark Heckmann
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
>
> ______________________________________________
> 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.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Circle 8.1.20 of 'The R Inferno'

http://www.burns-stat.com/pages/Tutor/R_inferno.pdf

gives the rules for argument matching.
When you see them explicitly set out there,
perhaps you will see why the matching
is as it is.

Pat

On 05/03/2012 09:24, Mark Heckmann wrote:
> I noticed that the argument names after the dots argument are not partially
matched.
>
> foo<- function(one, two, ...){
>    one + two
> }
>> foo(o=1, t=2)
> [1] 3
>
> foo<- function(one, ..., two){
>     one + two
> }
>
>> foo(o=1, t=2)
> Fehler in one + two : 'two' fehlt
>
>
> Can someone explain me the reason for this behavior?
>
> THX
> Mark
>
> ????????????????????????????????????
> Mark Heckmann
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
>
> ______________________________________________
> 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.
>
-- 
Patrick Burns
pburns at pburns.seanet.com
twitter: @portfolioprobe
http://www.portfolioprobe.com/blog
http://www.burns-stat.com
(home of 'Some hints for the R beginner'
and 'The R Inferno')