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https://issues.apache.org/jira/browse/MAHOUT-353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12851815#action_12851815
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Sean Owen commented on MAHOUT-353:
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I can change Cache to handle null values, but I think it's just disguising
another problem. The cache should never be unable to load the column vector,
since it should have generated a column vector for all. This is the underlying
issue.
Actually... my implementation of Retriever in RecommenderMapper is wrong. It
should never return null. It should treat this situation as an error and throw
an exception, which would be clearer. I should really change it to do that.
That doesn't solve the problem, but it makes it clearer where the problem is:
I think there is perhaps some issue in MapFilesMap? If I had to guess, this is
where the issue is. It should be reading from all the intermediate map files
that an earlier stage outputs to find column vectors. The fact that it's not
finding them suggests that's where the issue is.
I don't have your data or your setup so have some difficulty debugging from
here. If you are in a position to look into the code, can you examine whether
MapFilesMap seems to find all of those map files correctly, read them, etc.?
> 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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