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  1. Mahout
  2. MAHOUT-1020

The Cluster Evaluator is returning bad results

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: 0.6, 0.8
    • Fix Version/s: 0.8
    • Component/s: Clustering
    • Labels:
      None
    • Environment:

      Various environments and data sets. Mahout 0.6, 0.7, 0.8 trunk.

      Description

      Conversation with between Pat Ferrel and Jeff Eastman on the user list

      Hi Pat,

      I don't have a good answer here. Evidently, something in CDbw has become broken and you are the first to notice. When I run TestCDbwEvaluator, the values for k-means and fuzzy-k are clearly incorrect. The values for Canopy, MeanShift and Dirichlet are not so obviously incorrect but I remain suspicious. Something must have become broken in the recent clustering refactoring.

      From the method CDbwEvaluator.invalidCluster comment (used to enable pruning):

      • Return if the cluster is valid. Valid clusters must have more than 2 representative points,
      • and at least one of them must be different than the cluster center. This is because the
      • representative points extraction will duplicate the cluster center if it is empty.

      Oddly enough, inspection of the test log indicates that only k-means and fuzzy-k are not pruning clusters. Clearly some more investigation is needed. I will take a look at it tomorrow. In the mean time if you develop any additional insight please do share it with us.

      Thanks,
      Jeff

      On 5/17/12 3:53 PM, Pat Ferrel wrote:
      > I built a tool that iterates through a list of values for k on the same data and spits out the CDbw and ClusterEvaluator results each time.
      >
      > When the evaluator or CDbw prunes a cluster, how do I interpret that? They seem to throw out the same clusters on a given run. Also CDbw always returns an inter-cluster density of 0?

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            • Assignee:
              jeastman Jeff Eastman
              Reporter:
              pferrel Pat Ferrel
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              • Created:
                Updated:
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