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https://issues.apache.org/jira/browse/LUCENE-1372?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628480#action_12628480
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Paul Smith commented on LUCENE-1372:
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Having a Document sorted last because it has "zebra", even though it has
"apple" seems way incorrect. Yes it would be ideal if Lucene _could_ perform
the multi-term sort properly, but in the absence of an effective fix in the
short term, having the lexographically earlier term 'picked' as the primary
sort candidate is likely to generate results that match what users would expect
(even if it's not quite perfect).
Right now it looks blatantly silly at the presentation layer when one presents
the search results with their data, and show that "apple,zebra" appears last in
the list..
> Proposal: introduce more sensible sorting when a doc has multiple values for
> a term
> -----------------------------------------------------------------------------------
>
> Key: LUCENE-1372
> URL: https://issues.apache.org/jira/browse/LUCENE-1372
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.3.2
> Reporter: Paul Cowan
> Priority: Minor
> Attachments: lucene-multisort.patch
>
>
> At the moment, FieldCacheImpl has somewhat disconcerting values when sorting
> on a field for which multiple values exist for one document. For example,
> imagine a field "fruit" which is added to a document multiple times, with the
> values as follows:
> doc 1: {"apple"}
> doc 2: {"banana"}
> doc 3: {"apple", "banana"}
> doc 4: {"apple", "zebra"}
> if one sorts on the field "fruit", the loop in
> FieldCacheImpl.stringsIndexCache.createValue() (and similarly for the other
> methods in the various FieldCacheImpl caches) does the following:
> while (termDocs.next()) {
> retArray[termDocs.doc()] = t;
> }
> which means that we look over the terms in their natural order and, on each
> one, overwrite retArray[doc] with the value for each document with that term.
> Effectively, this overwriting means that a string sort in this circumstance
> will sort by the LAST term lexicographically, so the docs above will
> effecitvely be sorted as if they had the single values ("apple", "banana",
> "banana", "zebra") which is nonintuitive. To change this to sort on the first
> time in the TermEnum seems relatively trivial and low-overhead; while it's
> not perfect (it's not local-aware, for example) the behaviour seems much more
> sensible to me. Interested to see what people think.
> Patch to follow.
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