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https://issues.apache.org/jira/browse/SOLR-8337?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joel Bernstein closed SOLR-8337.
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Resolution: Fixed
> Add ReduceOperation and wire it into the ReducerStream
> ------------------------------------------------------
>
> Key: SOLR-8337
> URL: https://issues.apache.org/jira/browse/SOLR-8337
> Project: Solr
> Issue Type: Bug
> Reporter: Joel Bernstein
> Attachments: SOLR-8337.patch, SOLR-8337.patch, SOLR-8337.patch,
> SOLR-8337.patch, SOLR-8337.patch
>
>
> The current ReducerStream groups all documents that share the same key(s)
> into a list and emits a single Tuple that contains this list. There is no way
> to tell the ReducerStream to do something more interesting with groups, for
> example summing a column within a group, or joining tuples.
> This ticket adds a new type of operation called a ReduceOperation which is
> passed to the ReducerStream so that the reduce behavior can be specialized.
> The ReduceOperation has two methods:
> 1) operate(Tuple) : This is called once for each Tuple in a group. This
> method can be used to aggregate Tuples as they added to a group.
> 2) reduce() : This is called when the group keys change. This method returns
> a single Tuple which is output by the ReducerStream. The ReduceOperation must
> clear it's internal structures when reduce is called as well, to prepare for
> the next group.
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