[Rd] repeat bug report: as.factor argument to row / col fails if NULL dimnames

[Peter Dalgaard]

Prof Brian Ripley wrote:
> I have never seen the report in the repository.  There were problems 
> with R-bugs at around that time (most email submission was stalled for a 
> month or so).

Maybe, but I don't see a PR# on _any_ of Martin Morgan's posts...

> However, I think the problems are far more serious: the help page says
> 
>      Returns a matrix of integers indicating their column number in a
>      matrix-like object.
> ...
> 
> as.factor: a logical value indicating whether the value should be
>           returned as a factor rather than as numeric.
> 
> Value:
> 
>      An integer matrix with the same dimensions as 'x' and whose
>      'ij'-th element is equal to 'j'.
> 
> There is no mention of using the column labels as the values and the 
> result was not even a matrix.  I certainly expected the factor levels to 
> be numeric.
> 
> I presume that the intention is to use the column labels (default 
> seq_len(nrow(x)) ) in place of the numbers, and to return a factor 
> matrix, so I have implemented that for col() and row().
> 
> However, I do wonder that anyone was using as.factor=TRUE given that it 
> did not do anything like what it was documented to.

There could, I suppose, be applications of the style

library(ISwR)
dd <- data.frame(count=c(caesar.shoe),
   caesar=row(caesar.shoe,as.factor=TRUE),
   size=col(caesar.shoe,as.factor=TRUE)) 
anova(glm(count~caesar*size,family=poisson,data=dd))

(as.data.frame.table is better in this case, I know). Notice that this 
will break if you change the value to a factor matrix.

It is not clear that a matrix is desired -- an alternative point of view 
is that when you request a factor, it is intended to be used along with 
long-format data.

> On Mon, 8 Dec 2008, Dan Davison wrote:
> 
>> This bug was reported to r-devel by Martin Morgan on 13th May 2008
>> (original email pasted below). However I couldn't locate it in the bug
>> tracker (with searches for row, col, as\.factor) It is still present
>> in today's svn version (rev 47115). I hope I'm doing something useful
>> by bringing it up again. I have not sent this to r-bugs, as I'm
>> concerned that not locating it in the bug tracker could be my failing.
>>
>> D

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