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https://issues.apache.org/jira/browse/FLINK-1269?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stephan Ewen closed FLINK-1269.
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Resolution: Abandoned
Closing this as abandoned due to long inactivity.
> Easy way to "group count" dataset
> ---------------------------------
>
> Key: FLINK-1269
> URL: https://issues.apache.org/jira/browse/FLINK-1269
> Project: Flink
> Issue Type: New Feature
> Components: API / DataSet
> Affects Versions: 0.7.0-incubating
> Reporter: Sebastian Schelter
> Assignee: Suneel Marthi
> Priority: Major
> Labels: stale-assigned
>
> Flink should offer an easy way to group datasets and compute the sizes of the
> resulting groups. This is one of the most essential operations in distributed
> processing, yet it is very hard to implement in Flink.
> I assume it could be a show-stopper for people trying Flink, because at the
> moment, users have to perform the grouping and then write a groupReduce that
> counts the tuples in the group and extracts the group key at the same time.
> Here is what I would semantically expect to happen:
> {noformat}
> def groupCount[T, K](data: DataSet[T], extractKey: (T) => K): DataSet[(K,
> Long)] = {
> data.groupBy { extractKey }
> .reduceGroup { group => countBy(extractKey, group) }
> }
> private[this] def countBy[T, K](extractKey: T => K,
> group: Iterator[T]): (K, Long) = {
> val key = extractKey(group.next())
> var count = 1L
> while (group.hasNext) {
> group.next()
> count += 1
> }
> key -> count
> }
> {noformat}
>
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