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https://issues.apache.org/jira/browse/MAHOUT-610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13009635#comment-13009635
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Sebastian Schelter commented on MAHOUT-610:
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yes it's fixed
> Not all Coocurrences provided to SimilarityReducer
> --------------------------------------------------
>
> Key: MAHOUT-610
> URL: https://issues.apache.org/jira/browse/MAHOUT-610
> Project: Mahout
> Issue Type: Bug
> Components: Collaborative Filtering, Math
> Reporter: Joris Geessels
> Assignee: Sebastian Schelter
> Fix For: 0.5
>
> Attachments: mahout-610.patch
>
>
> While doing some tests with the RecommenderJob, and more specifically the
> RowSimilarityJob, I noticed that in some cases not all cooccurences are used
> in the similarity calculations ( done in the SimilarityReducer class ).
> A RowPair object with (RowA=1,RowB=2) isn't considered the same as
> (RowA=2,RowB=1). This causes problems as CoocurencesMapper sometimes emits
> rowpairs in the first form and sometimes in the second form thus separating
> the cooccurences. If I'm right, this is due to the fact that ordering of the
> WeightedCoocurrenceArray for one column isn't guaranteed to be the same as
> for another column.
> The solution is very simple, either you can change the compare method of the
> RowPair class or you can adapt the CooccurencesMapper to enforce that RowA <
> RowB.
> Hope I've not missed something obvious, and that this is intended behavior.
> If this is the case, please enlighten me :-)
> Also, slightly off topic. While doing these tests, I've noticed that the
> predictions are all remarkably high and the RMSE on the movielens 100k
> dataset lies around 1,6.
> A bit to high if you ask me. Are these normal values or am I doing something
> wrong?
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