ItemRecommender documentation is vague on some details. about lenskit HOT 4 CLOSED

negative numbers are documented to indicate "no particular size requested" however, it is convention (which I want to rely on) that -1 should indicate "rank all items"

Hmm. I sympathize. However, I am very hesitant to increase the guarantees implementations are required to maintain.

It is not made clear that implementations are allowed to return fewer than the requested n items (such as if the item recommender enforces a constraint and cannot or will not return more items)

Definitely need to clear that up.

from lenskit.

Quoting you on PR997 on the subject of -1 == all:

It does. Actually, any negative value is supposed to be all.

Currently there is no "correct" way to ask for an absolute ranking that I can think of. I consider this a problem.

from lenskit.

Currently there is no "correct" way to ask for an absolute ranking that I can think of. I consider this a problem.

I do not automatically disagree.

In conversation with Qian, we've discussed the relationship of retrieval, ranking, and recommendation.

What would you think about specifying that -1 means 'recommend as many as possible'? Leaves the door open for some hypothetical recommender with a strong belief that 10 items are all you need, but much more strongly indicates that any recommender without such a belief should generate as long a list as it can.

from lenskit.

I like this resolution. I agree that not all recommenders can produce a complete list (I just built one that will provide a truncated list due to constraints)

So the changes:

• Document that recommenders are not guaranteed to return n items
• Document that negative means "as many as possible" which often implies "all", but not always.

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