[R] sweep() and recycling

[Robin Hankin]

Hi Heather

thanks for this.  (I have messed up quote level somewhere.  Sorry for 
that).


On Jun 20, 2005, at 02:01 pm, Heather Turner wrote:
>
>>>> Robin Hankin <r.hankin at noc.soton.ac.uk> 06/20/05 10:32am >>>
>> Hi
>>
>> [snip]
>> I would expect sweep() to give
>> me a warning if the elements don't recycle nicely
>
[snip]
>
>> behave as expected,   But
>>
>>
>> sweep(X,1,1:5,"+")
>>
>> and
>>
>>   sweep(X,2,1:5,"+")
>>
>>
>>
>> are identical!
>>
> ...which is also expected since the matrix is square. Perhaps the
>> following will help you see why:
>

> matrix(1:5,6,6)
>  matrix(1:5,6,6, byrow = TRUE)



Yes,  after thinking about your example for a few minutes, it was a bit 
foolish of me
to use a square matrix to illustrate this problem.
Thinking about it, it is the coincidence that ncol(X) %% n == 
nrow(X)%%n == 1 that
caused the phenomenon I remarked on [here n=length(x)].

I should have known better, as I use this phenomenon deliberately in 
magic square
construction! (although not by using  sweep()).

> I agree with your main point however, it would be useful if 'sweep'
> would give a warning when the length of the vector of statistics to be
> swept out was not a sub-multiple or multiple of the corresponding array
> dimension.


yes, that would be good.   Can anyone think of  a situation in which 
one would want to ignore
such a warning?  Conversely, does anyone deliberately use sweep() with
   non-recycling vector?

>
--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743