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https://issues.apache.org/jira/browse/MAHOUT-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13157672#comment-13157672
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Jake Mannix commented on MAHOUT-884:
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bq. The trick is that we want the vectors to come in right-to-left order at
each reducer, so that the output vector writes sequentially. See in Ricky Ho's
blog page, search for "Optimized reducer-side join". He uses a partitioner to
achieve this.
Yeah, you just do a secondary sort-by-value (using a custom partitioner and
comparator).
> Matrix Concatenate utility
> --------------------------
>
> Key: MAHOUT-884
> URL: https://issues.apache.org/jira/browse/MAHOUT-884
> Project: Mahout
> Issue Type: New Feature
> Components: Integration
> Reporter: Lance Norskog
> Priority: Minor
> Attachments: MAHOUT-884.patch, MAHOUT-884.patch
>
>
> Utility to concatenate matrices stored as SequenceFiles of vectors.
> Each pair in the SequenceFile is the IntWritable row number and a
> VectorWritable.
> The input and output files may skip rows.
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