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From Josh Wills <josh.wi...@gmail.com>
Subject Re: Aggregator properties
Date Mon, 12 Nov 2012 18:35:29 GMT
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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