js 根据数组长度如何生成数组？

Question

问题描述

两个数组嵌套循环，如何根据外层数组的长度生成,新的数组

问题出现的环境背景及自己尝试过哪些方法

第一个 数组arr中的 17和18 或许只有一个数或许是2个，当然 arr2 中对应的 time 也会是一个或者2个，然后根据这个数的个数，生成新的数组

相关代码

粘贴代码文本（请勿用截图）

数据：

{
    arr: ['17', '18'],
    arr2: [
        {
            time: '17',
            createTime: '20220217 00:00:00',
            inId: 111,
            runningCount: 202,
        },
        {
            time: '17',
            createTime: '20220217 00:05:00',
            inId: 112,
            runningCount: 220,
        },
        {
            time: '17',
            createTime: '20220217 00:10:00',
            inId: 113,
            runningCount: 210,
        },
        {
            time: '17',
            createTime: '20220217 00:15:00',
            inId: 114,
            runningCount: 52,
        },
        {
            time: '17',
            createTime: '20220217 00:20:00',
            inId: 115,
            runningCount: 12,
        },
        {
            time: '17',
            createTime: '20220217 00:25:00',
            inId: 116,
            runningCount: 72,
        },
        {
            time: '18',
            createTime: '20220217 00:00:00',
            inId: 117,
            runningCount: 120,
        },
        {
            time: '18',
            createTime: '20220217 00:05:00',
            inId: 118,
            runningCount: 32,
        },
        {
            time: '18',
            createTime: '20220217 00:10:00',
            inId: 119,
            runningCount: 82,
        },
        {
            time: '18',
            createTime: '20220217 00:15:00',
            inId: 120,
            runningCount: 42,
        },
        {
            time: '18',
            createTime: '20220217 00:20:00',
            inId: 121,
            runningCount: 92,
        },
        {
            time: '18',
            createTime: '20220217 00:25:00',
            inId: 122,
            runningCount: 32,
        },
    ]
}

想要的结构

{
    child1: [
        {
            time: '17',
            createTime: '20220217 00:00:00',
            inId: 111,
            runningCount: 202,
        },
        {
            time: '17',
            createTime: '20220217 00:05:00',
            inId: 112,
            runningCount: 220,
        },
        {
            time: '17',
            createTime: '20220217 00:10:00',
            inId: 113,
            runningCount: 210,
        },
        {
            time: '17',
            createTime: '20220217 00:15:00',
            inId: 114,
            runningCount: 52,
        },
        {
            time: '17',
            createTime: '20220217 00:20:00',
            inId: 115,
            runningCount: 12,
        },
        {
            time: '17',
            createTime: '20220217 00:25:00',
            inId: 116,
            runningCount: 72,
        },
        {
            time: '18',
            createTime: '20220217 00:00:00',
            inId: 117,
            runningCount: 120,
        },
    ],
    child2: [
        {
            time: '18',
            createTime: '20220217 00:00:00',
            inId: 117,
            runningCount: 120,
        },
        {
            time: '18',
            createTime: '20220217 00:05:00',
            inId: 118,
            runningCount: 32,
        },
        {
            time: '18',
            createTime: '20220217 00:10:00',
            inId: 119,
            runningCount: 82,
        },
        {
            time: '18',
            createTime: '20220217 00:15:00',
            inId: 120,
            runningCount: 42,
        },
        {
            time: '18',
            createTime: '20220217 00:20:00',
            inId: 121,
            runningCount: 92,
        },
        {
            time: '18',
            createTime: '20220217 00:25:00',
            inId: 122,
            runningCount: 32,
        },
    ]
}

你期待的结果是什么？实际看到的错误信息又是什么？

Answer 1

arr2.reduce((res,v) => {
  const index = arr.indexOf(v.time);
  if(index != -1) {
    (res[`child${index+1}`] ||= []).push(v)
  }
  return res;
}, {});

Answer 2

其实没有 arr 也可以把组分出来，直接对 arr2 进行分组就好。不过由于数据顺序的不确定性，直接对 arr2 分组可能出现一些与结果预期不符的情况：

• 18 在 17 的前面
• 有除了 17 和 18 之外的其他分组数据
• 只有 17 或者 18，甚至可能一个都没有

所以这么来看，可以理解为按 arr 进行处理，只把 arr 中存在的找出来并分组，而且按照 arr 中的数据顺序。如果某个 key 不存在于 arr2 中，那就直接给个 [] ……

const result = arr.map(() => []);
arr2.forEach(it => {
    const group = result[arr.indexOf(it.time)];
    group && group.push(it);
});

// 本来到这里就可以结束了，但是你想要的是 {child1: [], child2: []}
// 所以需要转换一下

const objResult = Object.fromEntries(result.map((group, index) => [`child${index + 1}`, group]));