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From Brian Arnold <barnold4...@gmail.com>
Subject Mahout Collaborative Filtering using a parallel matrix factorization
Date Fri, 25 Oct 2013 20:29:23 GMT
Hey Everyone,

I was hoping that someone could help me out with the
ParallelALSFactoirzationJob that I am trying to run.  I have been trying to
run this over a 27GB dataset of customer transaction data, and the job
keeps failing with a null pointer exception. I am running with Mahout 0.8
and the following parameters --lambda 0.05 --implicitFeedback true
--numFeatures 20 --numIterations 1 --tempDir temp/mahout_als
--numThreadsPerSolver 1.
ParallelALSFactorizationJob-ItemRatingVectorsMapper-Reducer completes fine,
ParallelALSFactorizationJob-TransposeMapper-Reducer completes fine,
ParallelALSFactorizationJob-AverageRatingMapper-Reducer completes fine, but
it fails on Recompute U, iteration (2/1), (1 threads, 5 features, implicit
feedback).


Here is the stacktrace I am receiving:

java.lang.RuntimeException: java.lang.NullPointerException
	at org.apache.hadoop.mapreduce.lib.map.MultithreadedMapper.run(MultithreadedMapper.java:149)
	at org.apache.mahout.cf.taste.hadoop.als.MultithreadedSharingMapper.run(MultithreadedSharingMapper.java:53)
	at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:763)
	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:363)
	at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
	at java.security.AccessController.doPrivileged(Native Method)
	at javax.security.auth.Subject.doAs(Subject.java:396)
	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1232)
	at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: java.lang.NullPointerException
	at org.apache.mahout.math.als.ImplicitFeedbackAlternatingLeastSquaresSolver.getYtransponseCuMinusIYPlusLambdaI(ImplicitFeedbackAlternatingLeastSquaresSolver.java:95)
	at org.apache.mahout.math.als.ImplicitFeedbackAlternatingLeastSquaresSolver.solve(ImplicitFeedbackAlternatingLeastSquaresSolver.java:51)
	at org.apache.mahout.cf.taste.hadoop.als.SolveImplicitFeedbackMapper.map(SolveImplicitFeedbackMapper.java:54)
	at org.apache.mahout.cf.taste.hadoop.als.SolveImplicitFeedbackMapper.map(SolveImplicitFeedbackMapper.java:29)
	at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:145)
	at org.apache.hadoop.mapreduce.lib.map.MultithreadedMapper$MapRunner.run(MultithreadedMapper.java:268)


Thanks so much!

Brian

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