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From "Fabian Hueske (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-925) Support KeySelector function returning Tuples
Date Fri, 27 Jun 2014 09:37:24 GMT

    [ https://issues.apache.org/jira/browse/FLINK-925?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045758#comment-14045758
] 

Fabian Hueske commented on FLINK-925:
-------------------------------------

Using a CustomComparable is not supported right now, however the second example, i.e., grouping
a Tuple2<MyComparable, Integer> on the Integer field, should work. Not sure why it fails
in this situation, but in principle it should be possible.

For this issue, I would focus on enabling KeySelectors that return Tuples of types which are
supported for grouping such as 

{code}
KeySelector<Tuple3<Integer, String, Double>, Tuple2<Integer, String>>
{code}

> Support KeySelector function returning Tuples
> ---------------------------------------------
>
>                 Key: FLINK-925
>                 URL: https://issues.apache.org/jira/browse/FLINK-925
>             Project: Flink
>          Issue Type: Improvement
>    Affects Versions: 0.6-incubating
>            Reporter: Fabian Hueske
>            Assignee: Tobias
>            Priority: Minor
>              Labels: starter
>
> KeySelector functions are used to extract keys on which DataSets can be grouped or joined.
> Currently, the keys types returned by KeySelector function are restricted to be comparable.
However, Flinks Tuple data types are not comparable (because this depends on the types of
its fields) which makes grouping and joining on composite keys difficult.
> We should change the signature of the groupBy(), join(), and coGroup() methods to allow
also non-comparable keys as return types of a KeySelector function. 
> Instead we will check at optimization time whether the returned type is comparable (which
is true for tuples if all elements are comparable).



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