Expanding partial names

On 3/7/06, Duncan Murdoch <murdoch at stats.uwo.ca> 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?

One trick I often use that is different from any of the suggestions I have seen so far (and is more transparent IMO) is the following:

lowlevel <- function(longname = 1) {
   cat("longname = ", longname, "\n")
}

wrapper <- function(...) {
    newArgs <-
        function(longname = 2, ...)
            list(longname = longname,
                 ...)
    do.call("lowlevel", newArgs(...))
}

which gives:

wrapper()

longname =  2 

wrapper(longname = 3)

longname =  3 

wrapper(long=20)

longname =  20 

wrapper(junk=3)

Error in lowlevel(longname = 2, junk = 3) : 
	unused argument(s) (junk ...)

-Deepayan