Development build. This page describes main, not a released package. The latest published Lodestar.Metrics is 0.3.0 — read its documentation.

Home › Metrics › Ranking metrics

ReciprocalRank

The one member of this package not verified against a reference. Every other number here replays a corpus frozen from Python; measured on scikit-learn 1.9.1, dir(sklearn.metrics) carries nothing matching reciprocal, so there is nothing to freeze. It ships under decision 0005, which also says what would retire that exception — a reference implementation worth capturing — and its definition is pinned by tests instead of by a corpus.

Mean reciprocal rank asks a narrower question than Ndcg: not how well the whole ordering was arranged, but how far a user had to read before finding anything useful. That makes it the right number when one good answer ends the search — a lookup, a question with one answer, a navigational query — and the wrong one when the reader will consume the whole list.

Because it counts only the first relevant document, it is blind to everything after it: a ranking that puts one relevant document first and buries nine others scores 1, the same as a ranking that found only that one. Report it beside an NDCG, not instead of one.

Members

Member	What it does
ReciprocalRank.Score	The mean of 1 / rank over the queries, where rank is the position of the first relevant document.