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https://issues.apache.org/jira/browse/MAHOUT-186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12763124#action_12763124
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Ted Dunning commented on MAHOUT-186:
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I don't quite understand the last comment, but generally if you want the top n
items in descending order, you keep a descending queue as you say in order to
make insertion efficient. It is generally good to cache the score of the least
element to speed comparisons even a little bit more.
Then when you want the results, you can just fill a list in reverse order
or just do this:
List r = new ArrayList(priorityQueue);
Collections.reverse(r);
Since this is pretty simple, I think I misunderstood the question.
> Classifier PriorityQueue returns erroneous results
> --------------------------------------------------
>
> Key: MAHOUT-186
> URL: https://issues.apache.org/jira/browse/MAHOUT-186
> Project: Mahout
> Issue Type: Bug
> Affects Versions: 0.1, 0.2
> Reporter: Robin Anil
> Assignee: Robin Anil
> Fix For: 0.2
>
> Attachments: MAHOUT-186.patch
>
>
> A simple test fails
> import org.apache.hadoop.util.PriorityQueue;
> PriorityQueue<ClassifierResult> queue = new ClassifierResultPriorityQueue(3);
> queue.insert(new ClassifierResult("label1", 5));
> queue.insert(new ClassifierResult("label2", 4));
> queue.insert(new ClassifierResult("label3", 3));
> queue.insert(new ClassifierResult("label4", 2));
> queue.insert(new ClassifierResult("label5", 1));
>
> assertEquals("Incorrect Size", 3, queue.size());
> log.info(queue.pop().toString());
> log.info(queue.pop().toString());
> log.info(queue.pop().toString());
> 09/10/07 16:58:39 INFO common.ClassifierResultPriorityQueueTest:
> ClassifierResult{category='label3', score=3.0}
> 09/10/07 16:58:39 INFO common.ClassifierResultPriorityQueueTest:
> ClassifierResult{category='label4', score=2.0}
> 09/10/07 16:58:39 INFO common.ClassifierResultPriorityQueueTest:
> ClassifierResult{category='label5', score=1.0}
> Expected label1 and label2 at the top
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