R help - Jun 2004 - Sloppy argument checking for named arguments

Christian --

This is not a bug, but a feature, and the dot is not the issue here.  R uses
partial argument matching on function arguments.  

  So:
> f <- function(foobar = 0){print(foobar)}
> f
function(foobar = 0){print(foobar)}
>
> f(fo=1)
[1] 1
> f(foo=1)
[1] 1
> f(foob=1)
[1] 1
> f(fooba=1)
[1] 1
> f(foon=1)
Error in f(foon = 1) : unused argument(s) (foon ...)
>
> f(foobar2=1)
Error in f(foobar2 = 1) : unused argument(s) (foobar2 ...)

This is mentioned in Venables & Ripley, MASS 4th edition on p. 55. I
can't
find it right now in the "Introduction to R" that is linked to on the
main
html help index page.   However, it is discussed in the R Language
Definition you can get to from the same page.

It seems like there must be an easier path to the information that I haven't
thought of.

Hope this helps,

Matt Wiener

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of
christianlederer at t-online.de
Sent: Thursday, June 03, 2004 12:20 AM
To: r-help at stat.math.ethz.ch
Subject: [R] Sloppy argument checking for named arguments



Dear R Gurus,

i recently noticed that R does sloppy argument checking for named
arguments, if the argument contains a dot.
Example:

 > f <- function(foo.bar=0) { print(foo.bar) }
 > f(foo=1)
[1] 1

I guess, this should be considered as a bug.
Anyway, the consequence is that bugs caused by typing errors
of this kind may are *very* hard to discover in complex progams.

Christian

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PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

It has already been pointed out that partial matching is a feature.

However, if the function uses ... then it will only match arguments 
exactly so if you want to write a function in which full matching only 
is accepted you can do it by putting in a dummy first argument of 
... and then issuing an error messaage if ... matches anything:

f <- function( ..., foo.bar = 0 )  { 
          stopifnot( length(list(...)) == 0 )
          print( foo.bar )
}

 
R> f( foo.bar = 1 )
[1] 1
R> f( foo = 1 )
Error: length(list(...)) == 0 is not TRUE


Christian Lederer <christianlederer <at> t-online.de> writes:

: 
: Dear R Gurus,
: 
: i recently noticed that R does sloppy argument checking for named
: arguments, if the argument contains a dot.
: Example:
: 
:  > f <- function(foo.bar=0) { print(foo.bar) }
:  > f(foo=1)
: [1] 1
: 
: I guess, this should be considered as a bug.
: Anyway, the consequence is that bugs caused by typing errors
: of this kind may are *very* hard to discover in complex progams.
: 
: Christian
: 
: ______________________________________________
: R-help <at> stat.math.ethz.ch mailing list
: https://www.stat.math.ethz.ch/mailman/listinfo/r-help
: PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
: 
:

Dear R Gurus,

i recently noticed that R does sloppy argument checking for named
arguments, if the argument contains a dot.
Example:

 > f <- function(foo.bar=0) { print(foo.bar) }
 > f(foo=1)
[1] 1

I guess, this should be considered as a bug.
Anyway, the consequence is that bugs caused by typing errors
of this kind may are *very* hard to discover in complex progams.

Christian

> From: Gabor Grothendieck
> 
> It has already been pointed out that partial matching is a feature.
> 
> However, if the function uses ... then it will only match arguments 
I believe a more precise description is: `no partial (or positional)
matching for arguments that come after the ...'.

Best,
Andy

> exactly so if you want to write a function in which full 
> matching only 
> is accepted you can do it by putting in a dummy first argument of 
> ... and then issuing an error messaage if ... matches anything:
> 
> f <- function( ..., foo.bar = 0 )  { 
>           stopifnot( length(list(...)) == 0 )
>           print( foo.bar )
> }
> 
>  
> R> f( foo.bar = 1 )
> [1] 1
> R> f( foo = 1 )
> Error: length(list(...)) == 0 is not TRUE
> 
> 
> Christian Lederer <christianlederer <at> t-online.de> writes:
> 
> : 
> : Dear R Gurus,
> : 
> : i recently noticed that R does sloppy argument checking for named
> : arguments, if the argument contains a dot.
> : Example:
> : 
> :  > f <- function(foo.bar=0) { print(foo.bar) }
> :  > f(foo=1)
> : [1] 1
> : 
> : I guess, this should be considered as a bug.
> : Anyway, the consequence is that bugs caused by typing errors
> : of this kind may are *very* hard to discover in complex progams.
> : 
> : Christian
> : 
> : ______________________________________________
> : R-help <at> stat.math.ethz.ch mailing list
> : https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> : PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> : 
> :
> 
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 
>