[MAHOUT-1020] The Cluster Evaluator is returning bad results

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.6, 0.8
• Fix Version/s: 0.8
• Component/s: classic

Environment

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

• Assignee: Jeff Eastman
• Reporter: Pat Ferrel
• Created: 23/May/12 23:15
• Updated: 31/Jan/24 22:14
• Resolved: 03/Jun/12 17:04

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?