Re: [R] How to define S4 methods for '['

From: McGehee, Robert <>
Date: Tue 21 Jun 2005 - 06:46:47 EST

setMethod("[","foo",function(x,i, j,
.,drop=TRUE)callGeneric(x@dat,i,j,drop=drop) )


You have a typo. Use ... instead of . (note ?"[").


Robert McGehee
Quantitative Analyst
Geode Capital Management, LLC
53 State Street, 5th Floor | Boston, MA | 02109 Tel: 617/392-8396 Fax:617/476-6389

-----Original Message-----
From: Berton Gunter [] Sent: Monday, June 20, 2005 4:25 PM
Subject: [R] How to define S4 methods for '['


This is a question about the S4 formal class system.

Suppose I have a class, 'foo', defined by:

setClass('foo',representation(dat='matrix', id='character') )

I wish to define a '[' method for foo that will extract from the 'dat' slot.
I would have thought that the following would work, but it doesn't:

setMethod("[","foo",function(x,i, j, .,drop=TRUE)callGeneric(x@dat,i, j,drop=drop) )

The only way I have succeeded in defining this method is using brute force
eval(parse(. :


This works. However, I am not able under any circumstances to pass the drop
argument -- it is ignored.

I would appreciate any pointers about how to do this properly. If this is
explicitly in the Green Book (I do not have it with me at the moment), that
will suffice.


Bert Gunter

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