我有一个这样的数组:
var arr1 = ["a", "b", "c", "d"];
我如何随机化/打乱它?
我有一个这样的数组:
var arr1 = ["a", "b", "c", "d"];
我如何随机化/打乱它?
当前回答
//doesn change array
Array.prototype.shuffle = function () {
let res = [];
let copy = [...this];
while (copy.length > 0) {
let index = Math.floor(Math.random() * copy.length);
res.push(copy[index]);
copy.splice(index, 1);
}
return res;
};
let a=[1, 2, 3, 4, 5, 6, 7, 8, 9];
console.log(a.shuffle());
其他回答
我认为还没有人给出一个可以在不扩展Array原型的情况下连接起来的解决方案(这是一个糟糕的做法)。使用稍微鲜为人知的reduce(),我们可以轻松地以允许串联的方式进行混洗:
var randomsquares = [1, 2, 3, 4, 5, 6, 7].reduce(shuffle).map(n => n*n);
您可能希望传递第二个参数[],否则如果尝试在空数组上执行此操作,则会失败:
// Both work. The second one wouldn't have worked as the one above
var randomsquares = [1, 2, 3, 4, 5, 6, 7].reduce(shuffle, []).map(n => n*n);
var randomsquares = [].reduce(shuffle, []).map(n => n*n);
让我们将shuffle定义为:
var shuffle = (rand, one, i, orig) => {
if (i !== 1) return rand; // Randomize it only once (arr.length > 1)
// You could use here other random algorithm if you wanted
for (let i = orig.length; i; i--) {
let j = Math.floor(Math.random() * i);
[orig[i - 1], orig[j]] = [orig[j], orig[i - 1]];
}
return orig;
}
您可以在JSFiddle或此处看到它的实际应用:
var shuffle=(all,one,i,orig)=>{如果(i!==1)返回全部;//你可以在这里使用其他随机算法for(设i=原始长度;i;i-){设j=数学地板(Math.random()*i);[原始[i-1],原始[j]]=[原始[j],原始[i-1]];}返回原点;}对于(变量i=0;i<5;i++){var randomarray=[1,2,3,4,5,6,7]。reduce(shuffle,[]);console.log(JSON.stringify(randomarray));}
无序排列到位
function shuffleArr (array){
for (var i = array.length - 1; i > 0; i--) {
var rand = Math.floor(Math.random() * (i + 1));
[array[i], array[rand]] = [array[rand], array[i]]
}
}
ES6纯,迭代
const getShuffledArr = arr => {
const newArr = arr.slice()
for (let i = newArr.length - 1; i > 0; i--) {
const rand = Math.floor(Math.random() * (i + 1));
[newArr[i], newArr[rand]] = [newArr[rand], newArr[i]];
}
return newArr
};
可靠性和性能测试
本页上的一些解决方案不可靠(它们只是部分随机化了阵列)。其他解决方案的效率明显较低。使用testShuffleArrayFun(见下文),我们可以测试阵列洗牌功能的可靠性和性能。
function testShuffleArrayFun(getShuffledArrayFun){
const arr = [0,1,2,3,4,5,6,7,8,9]
var countArr = arr.map(el=>{
return arr.map(
el=> 0
)
}) // For each possible position in the shuffledArr and for
// each possible value, we'll create a counter.
const t0 = performance.now()
const n = 1000000
for (var i=0 ; i<n ; i++){
// We'll call getShuffledArrayFun n times.
// And for each iteration, we'll increment the counter.
var shuffledArr = getShuffledArrayFun(arr)
shuffledArr.forEach(
(value,key)=>{countArr[key][value]++}
)
}
const t1 = performance.now()
console.log(`Count Values in position`)
console.table(countArr)
const frequencyArr = countArr.map( positionArr => (
positionArr.map(
count => count/n
)
))
console.log("Frequency of value in position")
console.table(frequencyArr)
console.log(`total time: ${t1-t0}`)
}
其他解决方案
其他解决方案只是为了好玩。
ES6纯,递归
const getShuffledArr = arr => {
if (arr.length === 1) {return arr};
const rand = Math.floor(Math.random() * arr.length);
return [arr[rand], ...getShuffledArr(arr.filter((_, i) => i != rand))];
};
ES6纯使用array.map
function getShuffledArr (arr){
return [...arr].map( (_, i, arrCopy) => {
var rand = i + ( Math.floor( Math.random() * (arrCopy.length - i) ) );
[arrCopy[rand], arrCopy[i]] = [arrCopy[i], arrCopy[rand]]
return arrCopy[i]
})
}
ES6纯使用array.reduce
function getShuffledArr (arr){
return arr.reduce(
(newArr, _, i) => {
var rand = i + ( Math.floor( Math.random() * (newArr.length - i) ) );
[newArr[rand], newArr[i]] = [newArr[i], newArr[rand]]
return newArr
}, [...arr]
)
}
var shuffle = function(array) {
temp = [];
originalLength = array.length;
for (var i = 0; i < originalLength; i++) {
temp.push(array.splice(Math.floor(Math.random()*array.length),1));
}
return temp;
};
Fisher Yates的另一个实现,使用严格模式:
function shuffleArray(a) {
"use strict";
var i, t, j;
for (i = a.length - 1; i > 0; i -= 1) {
t = a[i];
j = Math.floor(Math.random() * (i + 1));
a[i] = a[j];
a[j] = t;
}
return a;
}
使用underscore.js库。对于这种情况,方法_.shuffle()很好。以下是该方法的示例:
var _ = require("underscore");
var arr = [1,2,3,4,5,6];
// Testing _.shuffle
var testShuffle = function () {
var indexOne = 0;
var stObj = {
'0': 0,
'1': 1,
'2': 2,
'3': 3,
'4': 4,
'5': 5
};
for (var i = 0; i < 1000; i++) {
arr = _.shuffle(arr);
indexOne = _.indexOf(arr, 1);
stObj[indexOne] ++;
}
console.log(stObj);
};
testShuffle();