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https://issues.apache.org/jira/browse/MAHOUT-1508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13966279#comment-13966279
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Sebastian Schelter commented on MAHOUT-1508:
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I think we should maybe completely drop SparseRowMatrix. Its very dangerous to
use this implementation as it will always instantiate a Vector for each row
index. This kills performance when there are only a few non-zero rows (e.g.
for outer products of sparse vectors).
> SparseMatrix assign has huge performance problems
> -------------------------------------------------
>
> 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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