From pburns at pburns.seanet.com  Mon Dec  8 19:43:50 2003
From: pburns at pburns.seanet.com (Patrick Burns)
Date: Mon Dec  8 19:42:44 2003
Subject: [Rd] matrix coercion, logical -> character
References: <Pine.LNX.4.44.0312081607300.19904-100000@gannet.stats>
	<x2brqjp5aw.fsf@biostat.ku.dk>
Message-ID: <3FD4C666.9080302@pburns.seanet.com>

It seems another reason to make the change would be the
ability to work around the following feature:

 > lmat <- as.matrix(data.frame(a=c(FALSE, TRUE)))
 > lmat
  a     
1 "FALSE"
2 " TRUE"
 > mode(lmat) <- "logical"
 >
 > lmat
      a
1 FALSE
2    NA

Numeric, character and logical were mentioned.  Complex data
frames coerce to complex matrices already.

Apropos of this, it would be good to put a See Also "complex"
in the "numeric" help file and vice versa.

Patrick Burns

Burns Statistics
patrick@burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of S Poetry and "A Guide for the Unwilling S User")

Peter Dalgaard wrote:

>Prof Brian Ripley <ripley@stats.ox.ac.uk> writes:
>
>  
>
>>On 8 Dec 2003, Peter Dalgaard wrote:
>>
>>    
>>
>>>Anyone know whether this is intentional, and by which rationale?
>>>(R-devel on RedHat, but hardly new)
>>>      
>>>
>>It is documented:
>>
>>     'as.matrix' is a generic function. The method for data frames will
>>     convert any non-numeric column into a character vector using
>>     'format' and so return a character matrix.
>>    
>>
>
>and for apply:
>
>     If 'X' is not an array but has a dimension attribute, 'apply'
>     attempts to coerce it to an array via 'as.matrix' if it is
>     two-dimensional (e.g., data frames) or via 'as.array'.
>
>explains why apply(...., which) got in trouble
>
>  
>
>>Remember than not some long ago you could not have logical columns in data 
>>frames: they were coerced to factors.
>>
>>It would be easy to change to allow numeric, logical or character 
>>matrices.
>>    
>>
>
>Yes. That was the direction in which I was hinting. It does seem a bit
>like a leftover, and applying which() over a set of logical
>columns is not unlikely to be useful in practice.
>
>  
>


[Rd] matrix coercion, logical -> character
Patrick Burns