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https://issues.apache.org/jira/browse/LUCENE-3174?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Mark Nemeskey updated LUCENE-3174:
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Attachment: LUCENE-3174.patch
Almost completely removed idf from the Weights -- it still lingers in
explain(). The DocScorer factory methods now need both the Weight and the
Stats; that's the best I could do for now.
Robert: if you don't mind, I have included you patch in this one as well.
> Similarity.Stats class for term & collection statistics
> -------------------------------------------------------
>
> Key: LUCENE-3174
> URL: https://issues.apache.org/jira/browse/LUCENE-3174
> Project: Lucene - Java
> Issue Type: Sub-task
> Components: core/search
> Affects Versions: flexscoring branch
> Reporter: David Mark Nemeskey
> Assignee: David Mark Nemeskey
> Priority: Minor
> Fix For: flexscoring branch
>
> Attachments: LUCENE-3174.patch, LUCENE-3174.patch, LUCENE-3174.patch,
> LUCENE-3174_normalize_boost.patch
>
>
> In order to support ranking methods besides TF-IDF, we need to make the
> statistics they need available. These statistics could be computed in
> computeWeight (soon to become computeStats) and stored in a separate object
> for easy access. Since this object will be used solely by subclasses of
> Similarity, it should be implented as a static inner class, i.e.
> Similarity.Stats.
> There are two ways this could be implemented:
> - as a single Similarity.Stats class, reused by all ranking algorithms. In
> this case, this class would have a member field for all statistics;
> - as a hierarchy of Stats classes, one for each ranking algorithm. Each
> subclass would define only the statistics needed for the ranking algorithm.
> In the second case, the Stats class in DefaultSimilarity would have a single
> field, idf, while the one in e.g. BM25Similarity would have idf and average
> field/document length.
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