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| import { describe, expect, it } from "vitest"; | |
| import { dcgAtK, ndcgAtK, recallAtK } from "./metrics.ts"; | |
| describe("dcgAtK", () => { | |
| it("discounts relevance by position", () => { | |
| // A single relevant result at rank 1 scores higher than at rank 2. | |
| expect(dcgAtK([1, 0], 2)).toBe(1 / Math.log2(2)); | |
| expect(dcgAtK([0, 1], 2)).toBeCloseTo(1 / Math.log2(3)); | |
| }); | |
| it("ignores gains beyond k", () => { | |
| expect(dcgAtK([1, 1, 1], 1)).toBe(dcgAtK([1], 1)); | |
| }); | |
| }); | |
| describe("ndcgAtK", () => { | |
| it("is 1 when the relevant urls occupy the top ranks", () => { | |
| const relevant = ["a", "b"]; | |
| expect(ndcgAtK(["a", "b", "c"], relevant, 3)).toBeCloseTo(1); | |
| expect(ndcgAtK(["b", "a", "c"], relevant, 3)).toBeCloseTo(1); | |
| }); | |
| it("decreases as relevant urls sink", () => { | |
| const relevant = ["a", "b"]; | |
| const perfect = ndcgAtK(["a", "b", "c", "d"], relevant, 4); | |
| const half = ndcgAtK(["c", "a", "b", "d"], relevant, 4); | |
| const worst = ndcgAtK(["d", "c", "a", "b"], relevant, 4); | |
| expect(perfect).toBeCloseTo(1); | |
| expect(perfect).toBeGreaterThan(half); | |
| expect(half).toBeGreaterThan(worst); | |
| expect(worst).toBeGreaterThan(0); | |
| }); | |
| it("is 0 when no relevant url is ranked at all", () => { | |
| expect(ndcgAtK(["c", "d"], ["a", "b"], 2)).toBe(0); | |
| }); | |
| it("scores against an ideal top-k when there are more relevant urls than k", () => { | |
| // Three relevant urls, k=2: ideal top-2 is two relevant urls. | |
| const relevant = ["a", "b", "c"]; | |
| const topTwoRelevant = ndcgAtK(["a", "b", "c"], relevant, 2); | |
| const oneRelevantInTopTwo = ndcgAtK(["c", "d", "a"], relevant, 2); | |
| expect(topTwoRelevant).toBeCloseTo(1); | |
| expect(topTwoRelevant).toBeGreaterThan(oneRelevantInTopTwo); | |
| }); | |
| it("is 0 when there are no relevant urls to recall", () => { | |
| expect(ndcgAtK(["a", "b"], [], 2)).toBe(0); | |
| }); | |
| it("returns 0 for a non-positive k", () => { | |
| expect(ndcgAtK(["a"], ["a"], 0)).toBe(0); | |
| }); | |
| it("never exceeds 1 when a url is listed twice", () => { | |
| // A duplicate relevant url must not earn gain twice, which would push | |
| // nDCG above 1 and mask a regression. | |
| const ndcg = ndcgAtK(["u", "u", "x"], ["u"], 3); | |
| expect(ndcg).toBeLessThanOrEqual(1); | |
| expect(ndcg).toBeGreaterThan(0); | |
| }); | |
| }); | |
| describe("recallAtK", () => { | |
| it("is the fraction of relevant urls in the top-k", () => { | |
| const relevant = ["a", "b", "c"]; | |
| expect(recallAtK(["a", "b", "d"], relevant, 3)).toBeCloseTo(2 / 3); | |
| expect(recallAtK(["a", "b", "c", "d"], relevant, 4)).toBe(1); | |
| }); | |
| it("counts a relevant url only once even if it repeats", () => { | |
| expect(recallAtK(["a", "a", "a"], ["a", "b"], 3)).toBeCloseTo(0.5); | |
| }); | |
| it("is 0 when there are no relevant urls", () => { | |
| expect(recallAtK(["a"], [], 1)).toBe(0); | |
| }); | |
| }); | |