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From "Hoss Man (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1372) Proposal: introduce more sensible sorting when a doc has multiple values for a term
Date Thu, 04 Sep 2008 23:01:44 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1372?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628509#action_12628509
] 

Hoss Man commented on LUCENE-1372:
----------------------------------

bq. 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.

I'm not following this argument.  Will it be less silly when {zebra,apple} sorts before {banana}
?

If we're going to break backwards compatibility for FieldCache users, let's break it completely
and make the code throw a RuntimeException when it sees that retArray[termDocs.doc()] is non-null
... that way we are quickly alerting the client code that they are doing something very, very
wrong.

> 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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