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https://issues.apache.org/jira/browse/FLINK-970?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14058693#comment-14058693
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Fabian Hueske commented on FLINK-970:
-------------------------------------
Sorry, I confused the use cases.
1) For the first n of each group, Stephan is of course right. Combine for the
first n of each group in each partition and then reduce to the first n of each
group in the Reducer.
2) For the first n of the whole data set, we can use a Map where each map
(roughly) emits n / dop elements.
> Implement a first(n) operator
> -----------------------------
>
> Key: FLINK-970
> URL: https://issues.apache.org/jira/browse/FLINK-970
> Project: Flink
> Issue Type: New Feature
> Reporter: Timo Walther
> Assignee: Chesnay Schepler
> Priority: Minor
>
> It is only syntactic sugar, but I had many cases where I just needed the
> first element or the first 2 elements in a GroupReduce.
> E.g. Instead of
> {code:java}
> .reduceGroup(new GroupReduceFunction<String, String>() {
> @Override
> public void reduce(Iterator<String>
> values, Collector<String> out) throws Exception {
> out.collect(values.next());
> }
> })
> {code}
> {code:java}
> .first()
> {code}
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