Optimize getNumUsersWithPreferenceFor(long... itemIDs)
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Key: MAHOUT-423
URL: https://issues.apache.org/jira/browse/MAHOUT-423
Project: Mahout
Issue Type: Improvement
Components: Collaborative Filtering
Affects Versions: 0.3
Reporter: Jonathan Young
I ran a simple collaborative filtering application using a
GenericBooleanPrefDataModel built from (a subset of) the Netflix data, Tanimoto
similarity, and the GenericItemBasedRecommender, and then called
recommender.mostSimilarItems() (a lot).
Profiling indicated that the majority of the time was spent in
GenericBooleanPrefDataModel.getNumUsersWithPreferenceFor(long... itemIDs). The
version in GenericDataModel is optimized for the cases of one and two itemIDs,
but the version in GenericBooleanPrefDataModel always computes the intersection
set.
I can create a patch which optimizes the two cases of itemIDs.length == 1 and
itemIDs.length == 2 (similar to the version in GenericDataModel), but perhaps
the code should be refactored if these are really the most common cases.
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