Filter the corpus before choosing Top K

WHAT YOU WILL BUILD

A counterexample showing how filtering only after Top K can leave an empty result.

Ranking and eligibility answer different questions. A passage can score highly and still belong to another tenant or an obsolete version. The exercise compares selecting from eligible records with filtering a globally truncated result.

FOLLOW ALONG

Work through the example.

1. 01

   Inspect the candidate pool

   The highest-scoring record belongs to tenant B. Tenant A's old policy is second; its current policy is third. The request is for tenant A's current content only.

2. 02

   Run the post-filter baseline

   Take the global top result and then check eligibility. The only candidate is rejected, leaving zero results even though a valid current policy exists.

3. 03

   Run the eligible-corpus search

   Filter by tenant and current version first, then rank. The valid current-policy record is returned. The printed results show why these two orders are not equivalent.

4. 04

   Carry the boundary into an integration

   When using a database, apply trusted access constraints in its query and check its filtered-search behavior. Test strict filters, no eligible results, deleted records, and current-version changes with representative data.

THE COMPLETE LAB

Run it locally.

Run this command from the folder containing your downloaded file:

node vector-filtering.mjs

// SaveMyToken local lab. Run with Node.js 22 or newer.
import assert from "node:assert/strict";

// Exact dot-product ranking over toy vectors, not an ANN index.
const query = [1, 0];
const records = [
  { id: "other-tenant", tenant: "B", current: true, vector: [1, 0] },
  { id: "old-policy", tenant: "A", current: false, vector: [0.99, 0.01] },
  { id: "current-policy", tenant: "A", current: true, vector: [0.8, 0.2] },
];
const score = row => row.vector.reduce((sum, x, i) => sum + x * query[i], 0);
const rank = rows => [...rows].sort((a, b) => score(b) - score(a));
const eligible = row => row.tenant === "A" && row.current;
const postFilter = rank(records).slice(0, 1).filter(eligible);
const preFilter = rank(records.filter(eligible)).slice(0, 1);
assert.equal(postFilter.length, 0);
assert.equal(preFilter[0].id, "current-policy");
console.log("Filter after top 1:", postFilter.length, "results");
console.log("Filter before top 1:", preFilter[0].id);

Expected output for the unchanged example

Filter after top 1: 0 results
Filter before top 1: current-policy

The assertions also check the baseline behavior. After changing an input, predict the result and update the relevant assertion.

EXPLAIN WHAT YOU LEARNED

Interview practice

Try answering aloud before opening the reference answer. These are original learning questions, not a record of any employer's interviews.