Github user srowen commented on the pull request:
https://github.com/apache/spark/pull/597#issuecomment-42269236
Can I make a tiny suggestion to map from ratings to weights with something
like "rating - 2.5" instead of "rating - 3"? So that 3 becomes a small positive
value like 0.5?
There is an argument that even neutral ratings are weak positive
interactions; to have even consumed the item to be able to rate it means you
had an interest.
But more than that, the semantics of 0 in this expanded world of
non-positive weights are "the same as never having interacted at all" -- which
doesn't quite fit. I don't know if the intermediate sparse representations do
this internally, at the moment, but it's possible that 0 values are ignored
when constructing the sparse representation, because the 0s are implicit. This
would be a problem, at least, a theoretical one.
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