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From Sebastian Schelter <ssc.o...@googlemail.com>
Subject Re: Mahout Collaborative Filtering using a parallel matrix factorization
Date Sun, 27 Oct 2013 19:53:32 GMT
Hi Brian,

That error looks strange, could you try to run it on a toy dataset and
see if you get the same error?

--sebastian

On 25.10.2013 22:29, Brian Arnold wrote:
> 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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