How to avoid function masking

-----Original Message-----
From: Roger D. Peng [mailto:rpeng@stat.ucla.edu]
Sent: Thursday, May 22, 2003 2:40 PM
To: Warnes, Gregory R
Cc: 'R-devel@stat.math.ethz.ch'
Subject: Re: [Rd] How to avoid function masking


I believe recent R-devel has a `pos' argument to library() which lets 
you attach a package in a certain position.  Can't think of anything 
else though.

-roger

Warnes, Gregory R wrote:

Hi All,

I've been working on updating the 'genetics' package.  As a 

consequence of

the upgrade, .First.lib() looks like:

	.First.lib <- function(libname, pkgname) 
	{
	    if (!require(combinat)) 
	        warning("Unable to load 'combinat' library.  Function
`diseq.ci' will fail.")
	    require(gregmisc)
	    genotype <- get("genotype",pos="package:genetics")
	}

the First.lib of the "gregmisc" package in turn does 
	require("MASS")
which defines a data set "genotype" which masks the 

"genotype" function in

my genetics library.

Is there any clean way to load libraries in .First.lib 

while preventing this

kind of masking?  Ideally, there would be something like

	require("gregmisc", top=FALSE)

which would load the library (and any libraries it loads) 

into the *third*

position rather than the second position of the search path 

(.GlobalEnv is

in the first slot)?   Actually, does it make sense in 

general to have

top=FALSE be  the default behavior when loading packages 

from .First.lib to

avoid masking of this type?

For the moment I'm doing :

	.First.lib <- function(libname, pkgname) 
	{
	    if (!require(combinat)) 
	        warning("Unable to load 'combinat' library.  Function
`diseq.ci' will fail.")
	    require(gregmisc)
	    assign("genotype", get("genotype",pos="package:genetics"),
pos=.GlobalEnv )
	}

but this is a hack and doesn't solve the general problem.

-Greg



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