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https://issues.apache.org/jira/browse/MAHOUT-456?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895890#action_12895890
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Ted Dunning commented on MAHOUT-456:
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I haven't measured the effect, but I have seen rumblings about clone eating
more time than does allocation and copying. These rumblings make me leery of
using clone in any code where I care about speed.
Does anybody have anything more than vague suspicions on this point?
See here for instance for some old back and forth on this:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6195753
> RowSimilarityJob should not produce SequentialAccessSparseVectors
> -----------------------------------------------------------------
>
> Key: MAHOUT-456
> URL: https://issues.apache.org/jira/browse/MAHOUT-456
> Project: Mahout
> Issue Type: Improvement
> Components: Math
> Reporter: Sebastian Schelter
> Attachments: MAHOUT-456-2.patch, MAHOUT-456.patch, MAHOUT-456.patch,
> MAHOUT-456.patch
>
>
> RowSimilarityJob currently produces SequentialAccessSparseVectors with
> cardinality Integer.MAX_VALUE wrapped inside VectorWritables.
> It should better produce RandomAccessSparseVectors as some methods like
> assign(Vector) are very slow on such SequentialAccessSparseVectors.
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