Clustering_with_Hadoop

Introduction

The MapReduce paradigm was explored for knowledge discovery from nuclear reactor simulation data, as it is imminent that this data will quickly become large-scale. Hadoop, an open-source implementation of MapReduce, was used for this study.

For preliminary investigation, k-Means clustering, available from Mahout was employed. The results were similar to the ones we published in the paper, "Knowledge Discovery from Nuclear Reactor Simulation Data".

Process

• Here are the steps, we used for working with Hadoop:
• • Successfully install Hadoop from [<http://hadoop.apache.org/>]. I used the instructions from http://www.michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-singl... to install Hadoop on my laptop as a single node cluster. My laptop was running on Fedora 17.
• • The database used was HDFS - Hadoop Distributed File System http://hadoop.apache.org/docs/r1.0.4/mapred_tutorial.html.... A helpful tutorial on HDFS would be http://developer.yahoo.com/hadoop/tut.../module2.html.
• • Successfully install Mahout from [<http://mahout.apache.org/>].For examples on how to run various machine learning algorithms on mahout, are found at /mahout/examples/bin.
• • Put the requisite data for analysis on HDFS.
• • My data files are in the .csv format. Mahout's kmeans clustering expects the data to be formatted into a mahout specific SequenceFile format. A Java utility was written to convert our data into dense sequence file format, as needed by the kmeans clustering algo. Please note that mostly the examples for kmeans in mahout work with text data, and work on converting it into sparse vector format https://cwiki.apache.org/MAHOUT/quick-tour-of-text-analysis-using-th.... However, this was not the case with our data.
• • Run kmeans with -cl option. An example is: mahout kmeans -i /data/diff_unc_trans_seq/part-m-00000 -o /data/diff_unc_trans_kmeans_op -x 20 -k 2 -c /data/analysis_clusters -cl

Help for the various command line options for kmeans can be found at: https://cwiki.apache.org/MAHOUT/k-means-commandline.html....

• • Get the clusteredPoints directory out of HDFS to local directory.
• • Run mahout seqdumper to output them. An example is: mahout seqdumper -i /data/diff_unc_trans_kmeans_op/clusteredPoints/part-m-00000 -o ~/Data_orig/diff_unc_trans_hadoop_op/.
• • This can be further processed for analysis.

Resources

For more information on Hadoop, see their website, which contains many useful resources, including a tutorial on how to use Hadoop.

More details on Mahout and its uses can be found at the Apache Mahout website. The developers keep the website very well maintained, and you can find a great introduction to k-Means clustering, in addition to information on many other methods.

Some helpful materials on MapReduce include:

• Chapter 2 of Mining of Massive Datasets by Anand Rajaraman and Jeffrey David Ullman.
• MapReduce: A Flexible Data Processing Tool, a seminal paper by Google Fellows Jeffrey Dean and Sanjay Ghemawat, published in 2010.