runsly 技术分享 2022-03-14

js随机数组，js随机洗牌算法

本文分享一个使用JavaScript实现随机洗牌算法，帮助你得到一个随机数组。假如有一个数组是这样子：

var arr1 = ["a", "b", "c", "d"];

如何随机打乱数组顺序，也即洗牌。有一个比较广为传播的简单随机算法：

function RandomSort (a,b){ return (0.5 - Math.random()); }

实际证明上面这个并不完全随机。随便一搜网上太多这种东西了，看一下stackoverflow上的一个高分回答，答案出自github上。
knuth-shuffle The Fisher-Yates (aka Knuth) shuffle for Browser and Node.js 下面一起看看上面说的这个算法，代码如下：

/*jshint -W054 */
(function (exports) {
  'use strict';

  // http://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array
  function shuffle(array) {
    var currentIndex = array.length
      , temporaryValue
      , randomIndex
      ;

    // While there remain elements to shuffle...
    while (0 !== currentIndex) {

      // Pick a remaining element...
      randomIndex = Math.floor(Math.random() * currentIndex);
      currentIndex -= 1;

      // And swap it with the current element.
      temporaryValue = array[currentIndex];
      array[currentIndex] = array[randomIndex];
      array[randomIndex] = temporaryValue;
    }

    return array;
  }

  exports.knuthShuffle = shuffle;
}('undefined' !== typeof exports && exports || 'undefined' !== typeof window && window || global));

作者推荐使用浏览器写法：

(function () {
  'use strict';

  var a = [2,11,37,42]
    , b
    ;

  // The shuffle modifies the original array
  // calling a.slice(0) creates a copy, which is assigned to b
  b = window.knuthShuffle(a.slice(0));
  console.log(b);
}());

Nodejs：

npm install -S knuth-shuffle

(function () {
  'use strict';

  var shuffle = require('knuth-shuffle').knuthShuffle
    , a = [2,11,37,42]
    , b
    ;

  // The shuffle modifies the original array
  // calling a.slice(0) creates a copy, which is assigned to b
  b = shuffle(a.slice(0));
  console.log(b);
}());

还有其它从这个算法中变形去的，比如下面这个for循环的。其它的就不说了。

/**
 * Randomize array element order in-place.
 * Using Durstenfeld shuffle algorithm.
 */
function shuffleArray(array) {
    for (var i = array.length - 1; i > 0; i--) {
        var j = Math.floor(Math.random() * (i + 1));
        var temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
    return array;
}

使用ES2015（ES6）

Array.prototype.shuffle = function() {
  let m = this.length, i;
  while (m) {
    i = (Math.random() * m--) >>> 0;
    [this[m], this[i]] = [this[i], this[m]]
  }
  return this;
}

使用：