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