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https://issues.apache.org/jira/browse/SOLR-236?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12501550
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Yonik Seeley commented on SOLR-236:
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I guess adjacent collapsing can make sense when one is sorting by the field
that is being collapsed.
For the normal collapsing though, this patch appears to implement it by
changing the sort order to the collapsing field (normally not desired). For
example, if sorting by relevance and collapsing on a field, one would normally
want the groups sorted by relevance (with the group relevance defined as the
max score of it's members).
As far as how to do paging, it makes sense to rigidly define it in terms of
number of documents, regardless of how many documents are in each group. Going
back to google, it always displays the first 10 documents, but a variable
number of groups. That does mean that a group could be split across pages.
It would actually be much simpler (IMO) to always return a fixed number of
groups rather than a fixed number of documents, but I don't think this would be
less useful to people. Thoughts?
> Field collapsing
> ----------------
>
> Key: SOLR-236
> URL: https://issues.apache.org/jira/browse/SOLR-236
> Project: Solr
> Issue Type: New Feature
> Components: search
> Affects Versions: 1.2
> Reporter: Emmanuel Keller
> Attachments: field_collapsing_1.1.0.patch,
> SOLR-236-FieldCollapsing.patch, SOLR-236-FieldCollapsing.patch
>
>
> This patch include a new feature called "Field collapsing".
> "Used in order to collapse a group of results with similar value for a given
> field to a single entry in the result set. Site collapsing is a special case
> of this, where all results for a given web site is collapsed into one or two
> entries in the result set, typically with an associated "more documents from
> this site" link. See also Duplicate detection."
> http://www.fastsearch.com/glossary.aspx?m=48&amid=299
> The implementation add 3 new query parameters (SolrParams):
> "collapse.field" to choose the field used to group results
> "collapse.type" normal (default value) or adjacent
> "collapse.max" to select how many continuous results are allowed before
> collapsing
> TODO (in progress):
> - More documentation (on source code)
> - Test cases
> Two patches:
> - "field_collapsing.patch" for current development version (1.2)
> - "field_collapsing_1.1.0.patch" for Solr-1.1.0
> P.S.: Feedback and misspelling correction are welcome ;-)
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