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https://issues.apache.org/jira/browse/MAHOUT-1185?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen updated MAHOUT-1185:
------------------------------
Labels: (was: patch)
Priority: Minor (was: Major)
> MemoryDiffStorage.class has a bug for slope one algorithm which could cause
> incorrect recommendation results
> ------------------------------------------------------------------------------------------------------------
>
> Key: MAHOUT-1185
> URL: https://issues.apache.org/jira/browse/MAHOUT-1185
> Project: Mahout
> Issue Type: Bug
> Components: Collaborative Filtering
> Affects Versions: 0.7
> Environment: Ubuntu
> Reporter: Cunlu Zou
> Assignee: Sean Owen
> Priority: Minor
> Fix For: 0.8
>
> Attachments: MemoryDiffStorage.patch, MemoryDiffStorage.patch
>
> Original Estimate: 10m
> Remaining Estimate: 10m
>
> The function processOneUser(long averageCount, long userID) in the
> MemoryDiffStorage.class file contains a bug for calculating the itemAverage.
> Since the function tried to calculate the average difference among items (in
> a nested loop) and also the average individual item preference value in the
> same loop (the loop only from 0 to length-2, *for (int i = 0; i < length - 1;
> i++)*), the itemAverage variable does not count the last item's preference
> value for every users which could lead to an incorrect recommendation results.
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