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From "Sean Owen (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (MAHOUT-1185) MemoryDiffStorage.class has a bug for slope one algorithm which could cause incorrect recommendation results
Date Tue, 02 Apr 2013 09:37:18 GMT

     [ https://issues.apache.org/jira/browse/MAHOUT-1185?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sean Owen resolved MAHOUT-1185.
-------------------------------

       Resolution: Fixed
    Fix Version/s: 0.8

Done, this can actually be a one-liner change to loop to "i < length" in the outer loop.
                
> 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
>              Labels: patch
>             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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