[jira] [Resolved] (FLINK-622) Allow Reduce function to specify a starting element.

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[jira] [Resolved] (FLINK-622) Allow Reduce function to specify a starting element.

Shang Yuanchun (Jira)

     [ https://issues.apache.org/jira/browse/FLINK-622?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ufuk Celebi resolved FLINK-622.
-------------------------------

    Resolution: Duplicate

FLINK-758 has subsumed this issue. Actually, FLINK-758 kind of evolved to a duplicate for this issue, but since the discussion happened there, I'm closing this one.

Kudos to [~fhueske] for pointing this issue out earlier here.

> Allow Reduce function to specify a starting element.
> ----------------------------------------------------
>
>                 Key: FLINK-622
>                 URL: https://issues.apache.org/jira/browse/FLINK-622
>             Project: Flink
>          Issue Type: Improvement
>            Reporter: GitHub Import
>              Labels: github-import
>             Fix For: pre-apache
>
>
> We could extend ```ReduceFunction``` by a method ```T getStartElement()``` that returns the first element to give into the reduce function.
> By default this method returns ```null```. In this case, the first reduce call is done on the first and second elements of a group.
> If ```getStartElement()``` is overwritten in a ReduceFunction and it returns an object, the first reduce call is done on the start element and the first element.
> Right now, the Reduce function is only called if there are at least two elements in a group. Having the ```getStartElement()``` method, the UDF could also be called for groups with only one element.
> What do you guys think?
> ---------------- Imported from GitHub ----------------
> Url: https://github.com/stratosphere/stratosphere/issues/622
> Created by: [fhueske|https://github.com/fhueske]
> Labels: enhancement, java api, user satisfaction,
> Created at: Fri Mar 21 14:54:34 CET 2014
> State: open



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