[R] rowSums() and is.integer()

[Robin Hankin]

On 21 Nov 2007, at 08:30, Prof Brian Ripley wrote:

> On Tue, 20 Nov 2007, Tim Hesterberg wrote:
>
>> I wrote the original rowSums (in S-PLUS).
>> There, rowSums() does not coerce integer to double.
>
> Actaully, neither does R.  It computes a double answer but does no  
> coercion per se.
>
>> However, one advantage of coercion is to avoid integer overflow.
>
> Indeed, as I told Robin Hankin privately, that was the design reason.
>


Brian Ripley also reminded me that the sum() of integers is an integer,
behaviour that I find desirable.

The reason for my starting this thread is that
sometimes I actually *want* sums of
integers to overflow: my interest is in exact computations
where I must be absolutely certain that there can be no rounding error.

If the sum cannot be represented
in integers, I want this fact to be flagged with extreme vigour as it  
signals what
might be catastrophic loss of precision.

At least, that's my current thinking.



best wishes


rksh


>>
>> Tim Hesterberg
>>
>>> ...  So, why does rowSums() coerce to double (behaviour
>>> that is undesirable for me)?
>>
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>
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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