cmpstr/dist/esm/metric/Jaccard.js

CmpStr is a lightweight, fast and well performing package for calculating string similarity

// CmpStr v3.0.1 dev-052fa0c-250614 by Paul Köhler @komed3 / MIT License
import { MetricRegistry, Metric } from './Metric.js';
import { Pool } from '../utils/Pool.js';

/**
 * Jaccard Index
 * src/metric/Jaccard.ts
 *
 * @see https://en.wikipedia.org/wiki/Jaccard_index
 *
 * The Jaccard Index (or Jaccard similarity coefficient) measures the similarity
 * between two sets by dividing the size of their intersection by the size of
 * their union. In string similarity, it is often used to compare sets of characters,
 * tokens, or n-grams. The result is a value between 0 and 1, where 1 means the
 * sets are identical and 0 means they have no elements in common.
 *
 * @module Metric/JaccardIndex
 * @author Paul Köhler (komed3)
 * @license MIT
 */
/**
 * JaccardIndex class extends the Metric class to implement the Jaccard Index algorithm.
 */
class JaccardIndex extends Metric {
  /**
   * Constructor for the JaccardIndex class.
   *
   * Initializes the Jaccard Index metric with two input strings or
   * arrays of strings and optional options.
   *
   * @param {MetricInput} a - First input string or array of strings
   * @param {MetricInput} b - Second input string or array of strings
   * @param {MetricOptions} [opt] - Options for the metric computation
   */
  constructor(a, b, opt = {}) {
    // Call the parent Metric constructor with the metric name and inputs
    // Metric is symmetrical
    super('jaccard', a, b, opt, true);
  }
  /**
   * Calculates the Jaccard Index between two strings.
   *
   * @param {string} a - First string
   * @param {string} b - Second string
   * @param {number} m - Length of the first string
   * @param {number} n - Length of the second string
   * @return {MetricCompute<JaccardRaw>} - Object containing the similarity result and raw values
   */
  compute(a, b, m, n) {
    // Acquire two sets from the Pool
    const [setA, setB] = Pool.acquireMany('set', [m, n]);
    // Fill setA and setB with unique characters from a and b
    for (const A of a) setA.add(A);
    for (const B of b) setB.add(B);
    // Calculate intersection size
    let intersection = 0;
    for (const c of setA) if (setB.has(c)) intersection++;
    // Calculate union size (setA + elements in setB not in setA)
    const union = setA.size + setB.size - intersection;
    // Release sets back to the pool
    Pool.release('set', setA, m);
    Pool.release('set', setB, n);
    // Return the result as a MetricCompute object
    return {
      res: union === 0 ? 1 : Metric.clamp(intersection / union),
      raw: { intersection, union }
    };
  }
}
// Register the Jaccard index in the metric registry
MetricRegistry.add('jaccard', JaccardIndex);

export { JaccardIndex };
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