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Date: Fri, 19 Feb 2010 23:56:27 +0000 (UTC)
From: "Ted Dunning (JIRA)" <jira@apache.org>
To: mahout-dev@lucene.apache.org
Subject: [jira] Commented: (MAHOUT-300) Solve performance issues with Vector
 Implementations
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    [ https://issues.apache.org/jira/browse/MAHOUT-300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12836053#action_12836053 ] 

Ted Dunning commented on MAHOUT-300:
------------------------------------

I think that the min and max functions need to check to see if the number of non-zero elements is < size.  If so, then the max element is Math.max(0, max) and the min element is Math.min(0, min).  This should subsume the case where there are no elements so I would just replace hasNoElements with a counter that you can then use to compare to the size.

> Solve performance issues with Vector Implementations
> ----------------------------------------------------
>
>                 Key: MAHOUT-300
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-300
>             Project: Mahout
>          Issue Type: Improvement
>    Affects Versions: 0.3
>            Reporter: Robin Anil
>             Fix For: 0.3
>
>         Attachments: MAHOUT-300.patch
>
>
> AbstractVector operations like times
>   public Vector times(double x) {
>     Vector result = clone();
>     Iterator<Element> iter = iterateNonZero();
>     while (iter.hasNext()) {
>       Element element = iter.next();
>       int index = element.index();
>       result.setQuick(index, element.get() * x);
>     }
>     return result;
>   }
> should be implemented as follows
>  public Vector times(double x) {
>     Vector result = clone();
>     Iterator<Element> iter = result.iterateNonZero();
>     while (iter.hasNext()) {
>       Element element = iter.next();
>       element.set(element.get() * x);
>     }
>     return result;
>   }

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