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From "Michael McCandless (JIRA)" <>
Subject [jira] [Commented] (LUCENE-1421) Ability to group search results by field
Date Thu, 12 May 2011 12:41:48 GMT


Michael McCandless commented on LUCENE-1421:

bq. But what if docid=2 had age=17 instead? How would we determine what value the group (for
hgid=1) should have for the "age" field?

That would depend on the group sort, right? If your group sort is age asc the lowest document
would be chosen.

OK, I see.  So the group is "represented" by the doc within it that
sorts highest according to the group sort, and any faceting on the
groups means faceting on that top doc's values, per group.  Neat.

bq. Or... would the group count +1 to age=10 and +1 to age=17 in that case?

You mean like a sum of all ages per group? That is interesting, but sounds more like a function
to me. This can be computed with a separated group collector. Wouldn't make sense to me, to
have this with a regular field facet.

Well, not sum, but multi-valued?  (Ie, as if this group were
represented by a doc that takes the union of all age values of docs
within it).

This way, if the user then does a drill-down by a specific age, the
number of groups then returned would match the facet count of that age
in the first query.

I agree we need to hash out these semantics :)

Bill could you open a separate Lucene issue, to work out the semantics
& impl for "post-grouping-faceting"?  Unfortunately, it's blocked by
factoring out the facet module (LUCENE-3079).

> Ability to group search results by field
> ----------------------------------------
>                 Key: LUCENE-1421
>                 URL:
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Search
>            Reporter: Artyom Sokolov
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 3.2, 4.0
>         Attachments: LUCENE-1421.patch, LUCENE-1421.patch, lucene-grouping.patch
> It would be awesome to group search results by specified field. Some functionality was
provided for Apache Solr but I think it should be done in Core Lucene. There could be some
useful information like total hits about collapsed data like total count and so on.
> Thanks,
> Artyom

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