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https://issues.apache.org/jira/browse/MAHOUT-802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13100305#comment-13100305
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Sebastian Schelter commented on MAHOUT-802:
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The non-distributed recommender code uses longs to identify users and items. In
order to stay compatible the distributed code has to support them too, although
our distributed matrix operations are always keyed by ints. That's why we need
the conversion.
> Start Phase doesn't properly work in RecommenderJob
> ---------------------------------------------------
>
> Key: MAHOUT-802
> URL: https://issues.apache.org/jira/browse/MAHOUT-802
> Project: Mahout
> Issue Type: Bug
> Reporter: Grant Ingersoll
> Assignee: Grant Ingersoll
> Priority: Minor
> Fix For: 0.6
>
> Attachments: MAHOUT-802.patch, MAHOUT-802b.patch
>
>
> I'm trying to run RecommenderJob and do --startPhase 2 since I have my prefs
> already in the right format. Unfortunately, when I do that, I get:
> {quote}
> java.lang.IllegalArgumentException: Number of columns was not correctly set!
> at
> com.google.common.base.Preconditions.checkArgument(Preconditions.java:88)
> at
> org.apache.mahout.math.hadoop.similarity.RowSimilarityJob$SimilarityReducer.setup(RowSimilarityJob.java:296)
> at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:174)
> at
> org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:648)
> at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:416)
> at
> org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:256)
> {quote}
> This appears to be due to the fact that the numberOfUsers variable defaults
> to 0 and is only set when phase 1 is run.
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