Completeness metric (ratio of provided recos at top k positions)

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Feature Description

We need to measure, how many items are actually recommended for users at top k positions out of all possible when Completeness = 100% (every user has all K items recommended).

Why this feature?

Not all models recommend full lists that were required. It is necessary to easily find cases with Completeness less then 100%.

Additional context

Other names might be: Filling or Delivery or Fulfillment or Sufficiency or smth else. But not Coverage. Coverage is mostly used for other cases.