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https://issues.apache.org/jira/browse/MAHOUT-1190?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13631336#comment-13631336
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Robin Anil commented on MAHOUT-1190:
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Here is a summary of the improvements across two sparsities (100:1, 10:1). At
10K cardinality DenseVectors are about 3x faster on CosineDistance than the
sparse format.
https://docs.google.com/spreadsheet/ccc?key=0AhewTD_ZgznddGFQbWJCQTZXSnFULUYzdURfWDRJQlE#gid=1
> SequentialAccessSparseVector function assignment is very slow
> -------------------------------------------------------------
>
> Key: MAHOUT-1190
> URL: https://issues.apache.org/jira/browse/MAHOUT-1190
> Project: Mahout
> Issue Type: Bug
> Reporter: Dan Filimon
> Attachments: MAHOUT-1190-1.patch, MAHOUT-1190.patch
>
>
> Currently when calling .assign() on a SASV with another vector and a custom
> function, it will iterate through it and assign every single entry while also
> referring it by index.
> This makes the process *hugely* expensive. (on a run of BallKMeans on the 20
> newsgroups data set, profiling reveals that 92% of the runtime was spent
> updating assigning the vectors).
> Here's a prototype patch:
> https://github.com/dfilimon/mahout/commit/63998d82bb750150a6ae09052dadf6c326c62d3d
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