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From: Aljoscha Krettek <aljoscha@apache.org>
Date: Wed, 22 Feb 2017 10:10:10 +0000
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Subject: Re: [DISCUSS] Should we supply a new Iterator instance for Functions
 with Iterable input(s) like CoGroupFunction ?
To: dev@flink.apache.org
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archived-at: Wed, 22 Feb 2017 10:10:23 -0000

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Hi,
this is probably an oversight. If it helps you implement the feature,
please go ahead and add a sub-issue for solving the Iterator problem.

Best,
Aljoscha

On Tue, 21 Feb 2017 at 16:13 Lin Li <lincoln.86xy@gmail.com> wrote:

> Hi,
>
>     When I try to implement
> https://issues.apache.org/jira/browse/FLINK-5498
> via "dataset.coGroup(another dataset)" with a generated
> CoGroupFunction.(CoGroupFunction
> interface: public void coGroup(Iterable<IN1> first, Iterable<IN2> second,
> Collector<O> out)
>
>      I couldn't get the right results, then I saw the backend Iterator did
> not supply a new instance when invoked the "Iterable.iterator()" after
> debugging.
> (see  org.apache.flink.api.common.operators.util.ListKeyGroupedIterator,
>  it differs from usual iterable collections in java which will implement
> the iterator() method that supply a new iterator instance for the
> collection. And this is not mentioned either in comments or document.)
>
> IMO, iterable collections' new iterator instance requirements probably
> useful for other cases, so is it necessary to add this feature?
> Greatful if someone can tell me the motivation that ListKeyGroupedIterator
> didn't supply a new iterator instance.
>
> What do you think?
>
> Best, Lincoln
>

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