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From Matthias Friedrich <m...@mafr.de>
Subject Re: Aggregator properties
Date Mon, 12 Nov 2012 18:41:52 GMT
Hmm, right, I didn't think about that. I'll add a warning.

Thanks,
  Matthias

On Monday, 2012-11-12, Josh Wills wrote:
> Not necessarily-- you can use a secondary sort to make a non-commutative
> aggregator deterministic. But we should have a warning to that effect.
> 
> J
> 
> 
> On Mon, Nov 12, 2012 at 10:12 AM, Matthias Friedrich <matt@mafr.de> wrote:
> 
> > Hi,
> >
> > I would guess that Aggregator implementations have to be associative
> > and commutative. Otherwise they can't be used in Combiners in a
> > deterministic way. Am I right?
> >
> > If this is the case I'd suggest we add a big fat warning to our
> > StringConcatAggregator, because string concatenation isn't
> > commutative. Or maybe even remove it from our core API because it's a
> > bad role model?
> >
> > Thanks,
> >   Matthias
> >

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