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Posted to dev@mahout.apache.org by "Sean Owen (JIRA)" <ji...@apache.org> on 2010/01/21 23:43:54 UTC
[jira] Updated: (MAHOUT-207) AbstractVector.hashCode() should not
care about the order of iteration over elements
[ https://issues.apache.org/jira/browse/MAHOUT-207?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Sean Owen updated MAHOUT-207:
-----------------------------
Resolution: Fixed
Status: Resolved (was: Patch Available)
> AbstractVector.hashCode() should not care about the order of iteration over elements
> ------------------------------------------------------------------------------------
>
> Key: MAHOUT-207
> URL: https://issues.apache.org/jira/browse/MAHOUT-207
> Project: Mahout
> Issue Type: Bug
> Components: Math
> Affects Versions: 0.2
> Environment: all
> Reporter: Jake Mannix
> Assignee: Grant Ingersoll
> Fix For: 0.3
>
> Attachments: MAHOUT-207.patch
>
>
> As was discussed in MAHOUT-165, hashCode can be implemented simply like this:
> {code}
> public int hashCode() {
> final int prime = 31;
> int result = prime + ((name == null) ? 0 : name.hashCode());
> result = prime * result + size();
> Iterator<Element> iter = iterateNonZero();
> while (iter.hasNext()) {
> Element ele = iter.next();
> long v = Double.doubleToLongBits(ele.get());
> result += (ele.index() * (int)(v^(v>>32)));
> }
> return result;
> }
> {code}
> which obviates the need to sort the elements in the case of a random access hash-based implementation. Also, (ele.index() * (int)(v^(v>>32)) ) == 0 when v = Double.doubleToLongBits(0d), which avoids the wrong hashCode() for sparse vectors which have zero elements returned from the iterateNonZero() iterator.
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