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https://issues.apache.org/jira/browse/SPARK-2278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14060677#comment-14060677
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Sean Owen commented on SPARK-2278:
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Where are keys replicated? I don't get that point. Keys can be what you like,
as can values. Values don't need to contain keys to sortByKey for example. You
can sort by fields of a composite key without copying anything. A function like
"employee => employee.name" does not copy the value employee in order to access
the name for sorting purposes.
groupBy does not (necessarily) operate on key-value pair data. You can easily
group any value by some function of the value. groupByKey does of course.
> groupBy & groupByKey should support custom comparator
> -----------------------------------------------------
>
> Key: SPARK-2278
> URL: https://issues.apache.org/jira/browse/SPARK-2278
> Project: Spark
> Issue Type: New Feature
> Components: Java API
> Affects Versions: 1.0.0
> Reporter: Hans Uhlig
>
> To maintain parity with MapReduce you should be able to specify a custom key
> equality function in groupBy/groupByKey similar to sortByKey.
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