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https://issues.apache.org/jira/browse/MAHOUT-906?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen updated MAHOUT-906:
-----------------------------

       Resolution: Fixed
    Fix Version/s: 0.6
         Assignee: Sean Owen
           Status: Resolved  (was: Patch Available)

OK, I do understand the different computation for "size". As is, it's 
equivalent to the original, so I used the patched version. For "numItems" I 
think the new formula will slightly overcount, as it is used. It only affects 
fall-out anyway, so I left it as-is.
                
> Allow collaborative filtering evaluators to use custom logic in splitting 
> data set
> ----------------------------------------------------------------------------------
>
>                 Key: MAHOUT-906
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-906
>             Project: Mahout
>          Issue Type: Improvement
>          Components: Collaborative Filtering
>    Affects Versions: 0.5
>            Reporter: Anatoliy Kats
>            Assignee: Sean Owen
>            Priority: Minor
>              Labels: features
>             Fix For: 0.6
>
>         Attachments: MAHOUT-906.patch, MAHOUT-906.patch, MAHOUT-906.patch, 
> MAHOUT-906.patch, MAHOUT-906.patch
>
>   Original Estimate: 48h
>  Remaining Estimate: 48h
>
> I want to start a discussion about factoring out the logic used in splitting 
> the data set into training and testing.  Here is how things stand:  There are 
> two independent evaluator based classes:  
> AbstractDifferenceRecommenderEvaluator, splits all the preferences randomly 
> into a training and testing set.  GenericRecommenderIRStatsEvaluator takes 
> one user at a time, removes their top AT preferences, and counts how many of 
> them the system recommends back.
> I have two use cases that both deal with temporal dynamics.  In one case, 
> there may be expired items that can be used for building a training model, 
> but not a test model.  In the other, I may want to simulate the behavior of a 
> real system by building a preference matrix on days 1-k, and testing on the 
> ratings the user generated on the day k+1.  In this case, it's not items, but 
> preferences(user, item, rating triplets) which may belong only to the 
> training set.  Before we discuss appropriate design, are there any other use 
> cases we need to keep in mind?

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