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https://issues.apache.org/jira/browse/SOLR-5027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13838882#comment-13838882
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Joel Bernstein commented on SOLR-5027:
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Hi Gabe,
What I was planning to implement first is group head selection based on min/max
value of a function output. After that would I was planning to implement group
head selection based on a combination of score and one other criteria. I'd like
to have function based collapse criteria by the Solr 4.7 release.
Joel
> Field Collapsing PostFilter
> ---------------------------
>
> Key: SOLR-5027
> URL: https://issues.apache.org/jira/browse/SOLR-5027
> Project: Solr
> Issue Type: New Feature
> Components: search
> Affects Versions: 5.0
> Reporter: Joel Bernstein
> Assignee: Joel Bernstein
> Priority: Minor
> Fix For: 4.6, 5.0
>
> Attachments: SOLR-5027.patch, SOLR-5027.patch, SOLR-5027.patch,
> SOLR-5027.patch, SOLR-5027.patch, SOLR-5027.patch, SOLR-5027.patch,
> SOLR-5027.patch, SOLR-5027.patch
>
>
> This ticket introduces the *CollapsingQParserPlugin*
> The *CollapsingQParserPlugin* is a PostFilter that performs field collapsing.
> This is a high performance alternative to standard Solr field collapsing
> (with *ngroups*) when the number of distinct groups in the result set is high.
> For example in one performance test, a search with 10 million full results
> and 1 million collapsed groups:
> Standard grouping with ngroups : 17 seconds.
> CollapsingQParserPlugin: 300 milli-seconds.
> Sample syntax:
> Collapse based on the highest scoring document:
> {code}
> fq=(!collapse field=<field_name>}
> {code}
> Collapse based on the min value of a numeric field:
> {code}
> fq={!collapse field=<field_name> min=<field_name>}
> {code}
> Collapse based on the max value of a numeric field:
> {code}
> fq={!collapse field=<field_name> max=<field_name>}
> {code}
> Collapse with a null policy:
> {code}
> fq={!collapse field=<field_name> nullPolicy=<null_policy>}
> {code}
> There are three null policies:
> ignore : removes docs with a null value in the collapse field (default).
> expand : treats each doc with a null value in the collapse field as a
> separate group.
> collapse : collapses all docs with a null value into a single group using
> either highest score, or min/max.
> The CollapsingQParserPlugin also fully supports the QueryElevationComponent
> *Note:* The July 16 patch also includes and ExpandComponent that expands the
> collapsed groups for the current search result page. This functionality will
> be moved to it's own ticket.
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