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From Jeff Eastman <>
Subject Re: CDbw and Evaluator results
Date Wed, 23 May 2012 13:27:46 GMT
Can you try this again using trunk? If there is no improvement I think a 
JIRA to investigate would be useful.

On 5/22/12 2:02 PM, Pat Ferrel wrote:
> I'm using mahout 0.6 and so may not be seeing the same results as you.
> I take it that the inter-cluster distance of 0 is a bug and pruning 
> should not happen very often?
> I haven't used this before so I'm not sure if my CDbw or Evaluator 
> results are wrong in other ways.
> Should I create a bug for this in Jira?
> On 5/17/12 2:33 PM, Jeff Eastman wrote:
>> 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?
>>> On 5/17/12 5:58 AM, Jeff Eastman wrote:
>>>> Yes, that is the paper I used to implement CDbw. I've tried it a 
>>>> few times along with the simpler ClusterEvaluator metrics I took 
>>>> from Mahout In Action and they look to be reasonable - see the 
>>>> tests - though I have no way to judge their absolute values. 
>>>> Anything you can contribute in this area would be most welcome. 
>>>> Perhaps a wiki page?
>>>> On 5/16/12 1:14 PM, Pat Ferrel wrote:
>>>>> The reference was in the code for 
>>>>> On 5/16/12 9:56 AM, Pat Ferrel wrote:
>>>>>> Thanks, I've been looking at that. Is there a description of how

>>>>>> to interpret those values? An academic paper maybe? The 
>>>>>> intra-cluster distance intuitively seems to correspond to 
>>>>>> something like cohesion. I don't get the intuition behind 
>>>>>> inter-cluster distances but Ted thinks they are the most important.
>>>>>> On 5/16/12 7:32 AM, Jeff Eastman wrote:
>>>>>>> Mahout has a ClusterEvaluator and a CDbwEvaluator that compute

>>>>>>> some quality metrics (inter-cluster distance, 
>>>>>>> intra-cluster-distance, ...) that you may find useful. Both 
>>>>>>> calculate a set of representative points from the clustering

>>>>>>> output and compute the (n^2) metrics over these points rather

>>>>>>> than all of the points in each cluster.
>>>>>>> On 5/15/12 4:46 PM, Pat Ferrel wrote:
>>>>>>>> So many questions about best k, how to choose t1 and t2,
>>>>>>>> much help is dimensional reduction would have clear answers
>>>>>>>> we had a way to judge the quality of clusters.
>>>>>>>> Various methods were discussed here for a time: 
>>>>>>>> Has there been any work on building a measure of quality?

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