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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