From jmc at research.bell-labs.com  Tue Sep  7 16:34:46 2004
From: jmc at research.bell-labs.com (John Chambers)
Date: Tue Sep  7 16:35:01 2004
Subject: [Rd] package methods different behaviour R1.9.1 patched and R2.0.0
References: <200409070948060366.039FB48D@mail.math.fu-berlin.de>
Message-ID: <413DC706.AC82153C@research.bell-labs.com>

It's not possible to tell what you're expecting or actually seeing from
this mail.   We need to see your code and the results, not your
interpretation of how as() is implemented.

Meanwhile, here's how a simple class that extends "matrix" works in
2.0.0

With the code:

 setClass("mat1", representation(id="character"), contains = "matrix")

 mm <- matrix(1:12,3,4)

 mmm <- new("mat1", mm, id = "numeric")

The result is:

R> as(mmm, "vector")
 [1]  1  2  3  4  5  6  7  8  9 10 11 12

Class "vector" is one of the basic R classes;  as explained in ?as, the
methods for these use the exisiting as.<class> functions, as.vector in
this case.  

The result is indeed the same as coercing mmm to "matrix" first and then
to vector

R> as(as(mmm, "matrix"), "vector")
 [1]  1  2  3  4  5  6  7  8  9 10 11 12

as one would expect, but the method for coercing class "mat1" does not
go through "matrix":

R> selectMethod("coerce", c("mat1", "vector"))
function (from, to, strict = TRUE) 
{
    value <- as.vector(from)
    if (strict) 
        attributes(value) <- NULL
    value
}
<environment: namespace:methods>



Wolski wrote:
> 
> Hi!
> 
> Concerning different behaviour between 1.9.1 patched and:
> R : Copyright 2004, The R Foundation for Statistical Computing
> Version 2.0.0 Under development (unstable) (2004-09-06), ISBN 3-900051-07-0
> 
> Subtitle:
> as(x,"vector"); x is of class "Massvector"; never enters setAs("Massvector","vector"...
> 
> The same code:
> 
> as(mvl[[1]],"vector")
> causes under R1.9.1 to enter the function
> setAs("Massvector","vector"
>       ,function(from)
> ...
> 
> This never happens under R2.0.0.
> 
> The class "Massvector" contains class "Matrix"
> 
> A phenomenological description of what happens instead with R2.0.0 is
> 
> as(as(mvl[[1]],"Matrix"),"vector")
> 
> and its not what I would expect.
> 
> Is this an intended behaviour in R2.0.0?
> 
> /E
> 
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

-- 
John M. Chambers                  
Bell Labs, Lucent Technologies    office: (908)582-2681
700 Mountain Avenue, Room 2C-282  fax:    (908)582-3340
Murray Hill, NJ  07974


[Rd] package methods different behaviour R1.9.1 patched and R2.0.0
John Chambers