Github user MLnick commented on the pull request:
https://github.com/apache/spark/pull/597#issuecomment-42125746
It is true that implicit prefs predict 0/1 (ie a "preference" matrix rather
than a "rating" matrix), but the ratings are taken as confidence levels
indicating preference (or in the case of negative ratings, lack of preference).
So already there is an implicit mapping of 1 if r > 0, 0 if r == 0, with the
actual rating being a confidence value in the case of r > 0.
So keeping ratings input as is, is a reasonable approach. Even better would
be to map low ratings to zero or perhaps even negative scores, as a low rating
would indicate a lack of preference certainly.
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