[jira] [Updated] (MAHOUT-881) Refactor TopItems to use Lucene's PriorityQueue and remove excessive sorting

["Grant Ingersoll (Updated) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAHOUT-881?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Grant Ingersoll updated MAHOUT-881:
-----------------------------------

    Attachment: MAHOUT-881.patch

This patch converts TopItems to use Lucene PQ and removes unnecessary sorts, etc.  It fails on one test due to the fact that the old code does not provide a total ordering on the SimilarUser object (it does not honor the x.compare(y) == 0 implies x.equals(y) suggestion of Comparable) which means that in the GenericUserBasedRecommenderTest.testMostSimilar() asserts that the returned item is #4, but my version returns #3, which has the same score as #4.  This is because I break ties using the id.
                
> Refactor TopItems to use Lucene's PriorityQueue and remove excessive sorting
> ----------------------------------------------------------------------------
>
>                 Key: MAHOUT-881
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-881
>             Project: Mahout
>          Issue Type: Improvement
>    Affects Versions: 0.6
>            Reporter: Grant Ingersoll
>            Assignee: Grant Ingersoll
>            Priority: Minor
>         Attachments: MAHOUT-881.patch
>
>
> TopItems.getTop*() all do a fair number of excessive operations that can be replaced by switching to using Lucene's PriorityQueue implementation, which is more efficient and faster than Java's built in PQ implementation.

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