From Waclaw.Marcin.Kusnierczyk at idi.ntnu.no  Tue Nov 11 20:42:08 2008
From: Waclaw.Marcin.Kusnierczyk at idi.ntnu.no (Wacek Kusnierczyk)
Date: Tue, 11 Nov 2008 20:42:08 +0100
Subject: [Rd] is.matrix
In-Reply-To: <f8e6ff050811111121u62cc1329s605ca0dcd521dfb2@mail.gmail.com>
References: <d8858f220811111020j233d4d98j502c0079ace644e7@mail.gmail.com>	<4919D240.4040904@acm.org>
	<f8e6ff050811111121u62cc1329s605ca0dcd521dfb2@mail.gmail.com>
Message-ID: <4919E010.8080603@idi.ntnu.no>

hadley wickham wrote:
>> |  is.matrix| returns |TRUE| if |x| is a matrix and has a |dim <dim.html>|
>> attribute of length 2) and |FALSE| otherwise
>>     
>
> That's confusing!  In what situations is x a matrix but does not have
> a dim attribute?
>
>   

x = matrix(1,1,1)
dim(x) = c(1,1,1)
is.matrix(x)
# no
is("matrix", x)
# no
is(x)
# hm...

following the last, there would be a situation in which an object is a
matrix (per is(...)) and has a dim attribute of length != 2, but is a
matrix (per is.matrix(...) and is("matrix", ...), consistently with the
docs).

(the redundant "vector" in is(x) could probably be removed?)

vQ



[Rd] is.matrix
Wacek Kusnierczyk