[jira] [Commented] (MAHOUT-2019) SparseRowMatrix assign ops user for loops instead of iterateNonZero and so can be optimized

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-2019?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16234281#comment-16234281 ] 

ASF GitHub Bot commented on MAHOUT-2019:
----------------------------------------

Github user rawkintrevo commented on the issue:

    https://github.com/apache/mahout/pull/342
  
    Is this ready to merge?


> SparseRowMatrix assign ops user for loops instead of iterateNonZero and so can be optimized
> -------------------------------------------------------------------------------------------
>
>                 Key: MAHOUT-2019
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-2019
>             Project: Mahout
>          Issue Type: Bug
>          Components: Math
>    Affects Versions: 0.13.0
>            Reporter: Pat Ferrel
>            Assignee: Pat Ferrel
>            Priority: Major
>             Fix For: 0.13.1
>
>
> DRMs get blockified into SparseRowMatrix instances if the density is low. But SRM inherits the implementation of method like "assign" from AbstractMatrix, which uses nest for loops to traverse rows. For multiplying 2 matrices that are extremely sparse, the kind if data you see in collaborative filtering, this is extremely wasteful of execution time. Better to use a sparse vector's iterateNonZero Iterator for some function types.



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