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https://issues.apache.org/jira/browse/FLINK-925?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045790#comment-14045790
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Tobias commented on FLINK-925:
------------------------------
Can you elaborate more on: "Currently, the keys types returned by KeySelector
function are restricted to be comparable. However, Flinks Tuple data types are
not comparable"
- - I understood that the groupBy() has to be working with Tuple datatypes.
-> There is a groupBy() method which works on Tuple data types.
Why does the "other" groupBy() method which works with KeySelectors lose its
restriction of comparable?
Additionally:
"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."
-> I don't see a restriction of the join() and coGroup() methods to comparable.
How are those restricted?
I think I need more insights to understand the whole picture.
Thank you.
> 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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