Message-ID: <3FD4C666.9080302@pburns.seanet.com>
Date: 2003-12-08T19:42:44Z
From: Patrick Burns
Subject: matrix coercion, logical -> character
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.
>
>
>