talisman/metrics/eudex.js

Straightforward fuzzy matching, information retrieval and NLP building blocks for JavaScript.

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.distance = distance;
exports.isSimilar = isSimilar;

var _eudex = require('../phonetics/eudex');

var _eudex2 = _interopRequireDefault(_eudex);

var _long = require('long');

var _long2 = _interopRequireDefault(_long);

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

/**
 * Helpers.
 */

// NOTE: this is somewhat hacky and some methods can retrieve this information
// in constant time rather than our linear time here. However, the massive
// use of functions from the 'long' library might not be as optimized
// by JavaScript engines.
/**
 * Talisman metrics/eudex
 * =======================
 *
 * JavaScript implementation of the distance & similarity functions using
 * Eudex hashes.
 *
 * [Reference]:
 * https://github.com/ticki/eudex
 *
 * [Author]:
 * @ticki (https://github.com/ticki)
 *
 * [Tags]: metric, string metric.
 */
function bits(number) {
  return new _long2.default((number.toString(2).match(/1/g) || []).length);
}

/**
 * Function returning the distance between two strings hashed by Eudex.
 *
 * @param  {mixed}  a - The first string.
 * @param  {mixed}  b - The second string.
 * @return {number}   - The distance.
 */
function distance(a, b) {
  var d = (0, _eudex2.default)(a).xor((0, _eudex2.default)(b));

  var sum = bits(d.and(0xFF));

  var toAdd = [bits(d.shiftRight(8).and(0xFF)).mul(2), bits(d.shiftRight(16).and(0xFF)).mul(4), bits(d.shiftRight(24).and(0xFF)).mul(8), bits(d.shiftRight(32).and(0xFF)).mul(16), bits(d.shiftRight(40).and(0xFF)).mul(32), bits(d.shiftRight(48).and(0xFF)).mul(64), bits(d.shiftRight(56).and(0xFF)).mul(128)];

  for (var i = 0, l = toAdd.length; i < l; i++) {
    sum = sum.add(toAdd[i]);
  }return sum.low;
}

/**
 * Function returning whether the two given strings are similar by appraising
 * the distance between their Eudex hash.
 *
 * @param  {mixed}   a - The first string.
 * @param  {mixed}   b - The second string.
 * @return {boolean}
 */
function isSimilar(a, b) {
  return distance(a, b) < 10;
}