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From "Hui Wen Han (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAHOUT-353) java.lang.NullPointerException in RecommenderMapper
Date Wed, 31 Mar 2010 11:54:27 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12851828#action_12851828
] 

Hui Wen Han commented on MAHOUT-353:
------------------------------------

there has one situation:

some user only has one item,
so in UserVectorToCooccurrenceMapper class
there is no output for this item ,

so can not Retrieve the similar item for this item in RecommenderMapper.

am I怀write ? 

> java.lang.NullPointerException in RecommenderMapper
> ---------------------------------------------------
>
>                 Key: MAHOUT-353
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-353
>             Project: Mahout
>          Issue Type: Bug
>          Components: Collaborative Filtering
>    Affects Versions: 0.4
>            Reporter: Hui Wen Han
>             Fix For: 0.4
>
>
> java.lang.NullPointerException
> 	at org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper$CooccurrenceCache.get(RecommenderMapper.java:169)
> 	at org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper$CooccurrenceCache.get(RecommenderMapper.java:154)
> 	at org.apache.mahout.cf.taste.impl.common.Cache.getAndCacheValue(Cache.java:125)
> 	at org.apache.mahout.cf.taste.impl.common.Cache.get(Cache.java:94)
> 	at org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper.map(RecommenderMapper.java:111)
> 	at org.apache.mahout.cf.taste.hadoop.item.RecommenderMapper.map(RecommenderMapper.java:52)
> 	at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:50)
> 	at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:358)
> 	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
> 	at org.apache.hadoop.mapred.Child.main(Child.java:170)

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