From charles.dupont at vanderbilt.edu  Tue Mar  7 18:08:41 2006
From: charles.dupont at vanderbilt.edu (Charles Dupont)
Date: Tue, 07 Mar 2006 11:08:41 -0600
Subject: [Rd] Expanding partial names
In-Reply-To: <440D9295.7090207@stats.uwo.ca>
References: <440D9295.7090207@stats.uwo.ca>
Message-ID: <440DBE19.6070308@vanderbilt.edu>

Duncan Murdoch wrote:
> I'm writing wrappers for some functions that change some of the default 
> arguments.  I'd rather not list all of the arguments for the low level 
> functions because there are about a dozen wrapper functions, and about 
> 20 arguments to lowlevel.  Instead I'm trying something like this:
> 
> lowlevel <- function(longname = 1) {
>    cat("longname = ", longname, "\n")
> }
> 
> wrapper <- function(...) {
>    newargs <- list(longname = 2)
>    newargs[names(list(...))] <- list(...)
>    do.call("lowlevel", newargs)
> }
> 
> This almost works:
> 
>  > wrapper()
> longname =  2
>  > wrapper(longname = 3)
> longname =  3
> 
> But it fails if I try to use partial argument matching:
> 
>  > wrapper(long=4)
> Error in lowlevel(longname = 2, long = 4) :
>          unused argument(s) (long ...)
> 
> because long isn't matched to longname.  Is there a reasonable way to do 
> this (e.g. using pmatch or charmatch) other than listing all the low 
> level arguments in the argument list to wrapper?
> 
> Duncan Murdoch

If all you are doing is changing the default values of some arguments
this should work.

wrapper <- lowlevel
formals(wrapper) <- replace(formals(lowlevel), c("longname"), list(2))

Charles



[Rd] Expanding partial names
Charles Dupont