[jira] [Created] (MAHOUT-1185) MemoryDiffStorage.class has a bug for slope one algorithm which could cause incorrect recommendation results

["Cunlu Zou (JIRA)" <ji...@apache.org>]

Cunlu Zou created MAHOUT-1185:
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             Summary: 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
             Fix For: 0.8


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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