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Subject [CONF] Apache Mahout > Top Down Clustering
Date Wed, 07 Dec 2011 11:06:01 GMT
Space: Apache Mahout (
Page: Top Down Clustering (

Edited by Paritosh Ranjan:
Top Down Clustering

Top Down clustering is a type of Hierarchical Clustering. It tries to find bigger clusters
first and then does fine grained clustering on these clusters. Hence the name Top Down.

Any clustering algorithm can be used to perform the Top Level Clustering ( finding bigger
clusters ) and the Bottom Level Clustering ( fine grained clustering on each of the top level
clusters). So, all clustering algorithms available in Mahout, other than the MinHash Clustering
algorithm ( which is a "Bottom Up" Clustering Algorithm ), are suitable to be used for Top
Down Clustering, on both Top Level and Bottom Level.

The top level clustering output needs to be post processed in order to identify all top level
clusters and, to group vectors into their respective top level clusters. So, that, the bottom
level clustering can execute on each of them.

The first step to execute the top down clustering, would be to run any clustering algorithm
of your choice, preferably with clustering parameters which will produce bigger clusters.
This would be the top level clustering.

Then, the output of this clustering should be post processed, to group them into respective
top level clusters. This can be done using *ClusterOutputPostProcessorDriver.*

*ClusterOutputPostProcessorDriver* has a run method

*run(Path input, Path output, boolean runSequential)*

The input parameter provided to run method is, _"the output path provided to the clustering
algorithm"_, which would be post processed. It is the path of the directory containing clusters-*-final
and clusteredPoints.

The output parameter provided to run method is _"the path where the post processed data would
be stored"_.

The runSequential parameter provided to run method is _"If set to true, post processes it
sequentially, else, uses, MapReduce to do it"_. Hint : If the clustering was done sequentially,
make it sequential, else vice versa.

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