vtils/utils/cartesianProduct.js

一个面向业务的 JavaScript/TypeScript 实用程序库。

var supportNewFunction = function () {
  try {
    return new Function('return 1')() === 1;
  } catch (err) {
    return false;
  }
}();

/**
 * 计算多个数组的笛卡尔积。
 *
 * @param arr 数组内容
 * @example
 * ```typescript
 * cartesianProduct([
 *   ['a', 'b'],
 *   [1, 2],
 * ])
 * // => [['a', 1], ['a', 2], ['b', 1], ['b', 2]]
 * ```
 */

export function cartesianProduct(arr) {
  if (!Array.isArray(arr)) {
    throw new Error('cartesianProduct expects an array');
  }
  if (!arr.length) {
    return [];
  }
  if (!Array.isArray(arr[0])) {
    throw new Error('set at index 0 must be an array');
  }
  return (supportNewFunction && arr.length < 100 ?
  // 在支持动态构造函数环境下，并且数组长度小于 100 时使用快速模式
  cartesianProductProviders.fast :
  // 否则使用通用模式，如：小程序、数组长度大于等于 100
  cartesianProductProviders.universal).run(arr);
}
var cartesianProductProviders = {
  // https://github.com/angus-c/just/blob/master/packages/array-cartesian-product/index.js
  universal: {
    run: function run(arr) {
      // initialize our product array
      var product = arr[0].map(function (v) {
        return [v];
      });
      for (var i = 1; i < arr.length; i++) {
        if (!Array.isArray(arr[i])) {
          throw new Error("set at index " + i + " must be an array");
        }
        product = cartesianProductProviders.universal.baseProduct(product, arr[i]);
      }
      return product;
    },
    baseProduct: function baseProduct(prevProduct, arr2) {
      // pre allocate all our memory
      var newProduct = new Array(prevProduct.length * arr2.length);
      for (var i = 0; i < prevProduct.length; i++) {
        for (var j = 0; j < arr2.length; j++) {
          // always provide array to array.concat for consistent behavior
          newProduct[i * arr2.length + j] = prevProduct[i].concat([arr2[j]]);
        }
      }
      return newProduct;
    }
  },
  // https://github.com/ehmicky/fast-cartesian/blob/main/src/main.js
  fast: {
    cache: Object.create(null),
    run: function run(arr) {
      var loopFunc = cartesianProductProviders.fast.getLoopFunc(arr.length);
      var result = [];
      loopFunc(arr, result);
      return result;
    },
    getLoopFunc: function getLoopFunc(length) {
      var cachedLoopFunc = cartesianProductProviders.fast.cache[length];
      if (cachedLoopFunc !== undefined) {
        return cachedLoopFunc;
      }
      var loopFunc = cartesianProductProviders.fast.mGetLoopFunc(length);
      cartesianProductProviders.fast.cache[length] = loopFunc;
      return loopFunc;
    },
    mGetLoopFunc: function mGetLoopFunc(length) {
      var prefixArr = [];
      var startArr = [];
      var middleArr = [];
      var endArr = [];
      for (var i = 0; i < length; i++) {
        prefixArr.push("if (!Array.isArray(arrays[" + i + "])) { throw new Error('set at index " + i + " must be an array') }");
        startArr.push("for (var i" + i + " = 0; i" + i + " < arrays[" + i + "].length; i" + i + "++) {");
        middleArr.push("arrays[" + i + "][i" + i + "]");
        endArr.push("}");
      }
      var prefix = prefixArr.join('\n');
      var start = startArr.join('\n');
      var middle = middleArr.join(',');
      var end = endArr.join('\n');
      return new Function('arrays', 'result', prefix + "\n" + start + "\nresult.push([" + middle + "])\n" + end);
    }
  }
};