有没有办法在JS中将数组随机化到一定长度？

Question

假设我有一个数组：

array1 = [1, 2, 3, 4, 5, ........, 50]

我想将该数组随机化为一个具有长度限制的新数组。

例如，如果我想从 array1 中得到一个只有 5 个数字长的随机数组，我可以得到：

var arrayLength = 5

randomizedArray = [6, 20, 45, 2, 13]

有没有办法用 Math.random 做到这一点？

Answer 1

您可以映射数组并将每个项目设置为Math.random() 乘以上限（四舍五入）的结果：

function generateRandomArray(length, RNGUpperBound){
  return new Array(length).fill().map(e => Math.round(Math.random() * RNGUpperBound))
}
console.log(generateRandomArray(5, 10));

Answer 2

只要范围 (0..60) 不是非常大，我就会洗牌和切片。将数组 shuffle 作为一个常用的工具是一个好主意。

// from https://stackoverflow.com/a/2450976/294949
function fyShuffle(array) {
  let currentIndex = array.length,  randomIndex;
  while (0 !== currentIndex) {
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex--;
    [array[currentIndex], array[randomIndex]] = [
      array[randomIndex], array[currentIndex]];
  }
  return array;
}

let range = 60;
let resultLength = 5;
let array1 = [ ...Array(range).keys() ]; // the OP array

fyShuffle(array1);
console.log(array1.slice(0, resultLength))

Answer 3

您可以迭代数组 5 次并使用 Math.random() 随机推送索引：

let array1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50];

let newLength = 5,
    newArray = [];

for (let i = 0; i < 5; i ++) {
  newArray.push(array1[Math.floor(Math.random()  * (array1.length - 1))]);
}

console.log(newArray);

但是，这不会避免推送两次或多次相同的项目。您可以先使用includes() 方法检查该项目是否已包含：

let array1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50];

let newLength = 5,
  newArray = [];

for (let i = 0; i < 5; i++) {
  let randomElem = null;
  // Check if element is already in the array
  do {
    randomElem = array1[Math.floor(Math.random() * (array1.length - 1))];
  }while(newArray.includes(randomElem));
  
  newArray.push(randomElem);
}

console.log(newArray);

Answer 4

其他人都已经讨论过执行此操作的正常方法。我只想说rando.js 非常适合这些东西。

//if you have to use an array
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50];
console.log(randoSequence(arr).map(a => a.value).slice(-5));

//or if you prefer to be kind to yourself
console.log(randoSequence(1, 50).slice(-5))

<script src="https://randojs.com/2.0.0.js"></script>

Answer 5

这里，代码应该添加n distinct values，而不是添加n values（如果需要的话），因为如果n接近数组的长度，则元素可能会重复。

这是一个简单的代码sn-p，没有导入任何新的node_module。

let array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50];
let newArrayLength = 10;
let newArray = [];

while (newArrayLength > 0) {
  const rndIndex = Math.floor(Math.random() * array.length);
  if (!newArray.includes(array[rndIndex])) {
  newArray.push(array[rndIndex]);
  newArrayLength--;
  }
}
console.log('newArray', newArray);

Answer 6

方法一：打乱整个数组，取前N个元素

您始终可以对整个数组进行洗牌，然后取出前 5 个元素。这会浪费时间和内存，但这仅适用于非常大的输入或性能存在问题的情况。

使用任何common method 来打乱数组：

function shuffle(array) {
    return array.map((value) => ({ value, sort: Math.random() }))
        .sort((a, b) => a.sort - b.sort)
        .map(({ value }) => value)
}

然后：

const arrayLength = 5;
const array1 = [1, 2, ..., 50];

const shuffled = shuffle(array1);
// take the first n elements from the shuffled array
const sample = shuffled.slice(0, arrayLength);

方法 2：使用库

许多库已经实现了类似的东西 - 您正在寻找的是一个 N 个元素的随机样本。例如，试试 lodash 的 sampleSize as discussed in this answer。