[jira] [Commented] (MAHOUT-1508) Performance problems with sparse matrices

["Sebastian Schelter (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-1508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13967454#comment-13967454 ] 

Sebastian Schelter commented on MAHOUT-1508:
--------------------------------------------

SparseMatrix.viewRow() only creates new objects if the requested row has no non-zero entry yet.

> Performance problems with sparse matrices
> -----------------------------------------
>
>                 Key: MAHOUT-1508
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1508
>             Project: Mahout
>          Issue Type: Bug
>          Components: Math
>            Reporter: Sebastian Schelter
>            Priority: Blocker
>             Fix For: 1.0
>
>
> I'm currently working with the new Scala DSL and running into a problem with SparseMatrix and SparseRowMatrix.
> The problem is that they don't implement a specialized assign(Matrix other, DoubleDoubleFunction f) function, but use the implementation from AbstractMatrix which loops through all (!) possible entries. 
> We have to fix this asap.



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