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https://issues.apache.org/jira/browse/MAHOUT-1086?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13466480#comment-13466480
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Ted Dunning commented on MAHOUT-1086:
-------------------------------------
OK. I seem to be able replicate the problem with
trunk@1380432 MAHOUT-1059 - Abstract the idea of a cached length
1cb76f01b9b504fdf33a7ef6e30afdbd7d3842ef
and not before. This change also introduces some changes to AbstractVector
that might be the issue.
The changes involved have to do with whether operations on sparse matrices
operated sparsely. For instance, like()
used to be this:
{code}
Vector result = like().assign(this);
{code}
This causes a dense iteration which is wrong. The new code does this instead:
{code}
Vector result;
if (isDense()) {
result = like().assign(this);
} else {
result = like();
Iterator<Element> i = this.iterateNonZero();
while (i.hasNext()) {
final Element element = i.next();
result.setQuick(element.index(), element.get());
}
}
{code}
The idea is that if the source of the data is sparse, we only need to assign
the non-zero elements since we know the newly minted destination will be zero
filled.
My feeling is that this code is correct, but there is a more complex change
later in the same diff that might have changed some results.
I will isolate these changes and see if I can determine what the changes were
and how they impact canopy stuff.
> Mean Shift Test Now Produces 4 Clusters
> ---------------------------------------
>
> Key: MAHOUT-1086
> URL: https://issues.apache.org/jira/browse/MAHOUT-1086
> Project: Mahout
> Issue Type: Bug
> Components: Clustering
> Affects Versions: 0.7
> Reporter: Jeff Eastman
>
> Something changed in Mahout around 9/6/12 that caused
> TestMeanShift.testCanopyEuclideanMRJobNoClustering to return 4 clusters
> rather than 3. All of the other tests using the same data still return 3
> clusters. No changes were made to any of the MeanShiftCanopy classes other
> than 1 formatting change to the driver so I'm at a loss to the cause.
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