Rationalize DataModel.getNumUsersWithPreferenceFor() API
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Key: MAHOUT-764
URL: https://issues.apache.org/jira/browse/MAHOUT-764
Project: Mahout
Issue Type: Improvement
Components: Collaborative Filtering
Affects Versions: 0.5
Reporter: Sean Owen
Assignee: Sean Owen
Priority: Minor
Fix For: 0.6
Attachments: MAHOUT-764.patch
DataModel has a method getNumUsersWithPreferenceFor(long... itemIDs). It does
what it says. However I think this is a suboptimal API (for which we have me to
blame).
- All calls to this involve 1 or 2 arguments only
- No implementation supports more than 2 arguments, which makes the signature
misleading
- All implementations internally have some logic like "if it's 1, do X, if it's
args, do Y, otherwise fail"
- Calling this method, which happens frequently, always incurs the overhead of
allocating a long[]
The change is simple: make this two methods, with one and two args
respectively. Implementations would then just split their current
implementation into these two methods.
There is no API change for callers, at all, if invoked with 1 or 2 args. I
assume callers are not trying 3+ args now, as it has never been supported.
It does involve a straightforward change to implementors of DataModel.
Open for comment?
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