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https://issues.apache.org/jira/browse/FLINK-925?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045928#comment-14045928
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Tobias commented on FLINK-925:
------------------------------
When I have a reduce function: ReduceFunction<Tuple2<Tuple2<String, Integer>,
Integer>>
I get an exception:
{color: red}
Exception in thread "main" java.lang.IllegalArgumentException: The field at
position 0 (Tuple2<String, Integer>) is no atomic key type.
at
eu.stratosphere.api.java.typeutils.TupleTypeInfo.createLeadingFieldComparator(TupleTypeInfo.java:225)
at
eu.stratosphere.api.java.typeutils.TupleTypeInfo.createComparator(TupleTypeInfo.java:117)
at
eu.stratosphere.compiler.postpass.JavaApiPostPass.createComparator(JavaApiPostPass.java:322)
{color}
Creating a comparator for the Tuple type fails.
Might coGroup not be restricted because it does not work with KeySelectors?
I will look into coGroup and see if and how it works there.
> 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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