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reduce使用场景

news 2025/8/12 23:26:28

一、介绍基本用法

二、使用场景

聚合，包括求和、求平均值、出现的次数等

1. 数组求和、求积、计算数组对象中某属性的总和

    const numbers = [1, 2, 3, 4, 5];let res = numbers.reduce((pre, cur, index) => {pre += cur;if (index === numbers.length - 1) {return pre / numbers.length;} else {return pre;}}, 0);console.log(res);

var data = [{subject: "math",score: 10,},{subject: "chinese",score: 20,},{subject: "english",score: 30,},];let res = data.reduce((pre, cur) => {return pre + cur.score;}, 0);console.log(res);

2. 数组去重

  let data = [1, 2, 3, 4, 1, 2, 3, 5, 6, 7, 8];let res = data.reduce((pre, cur) => {if (pre.includes(cur)) {return pre;} else {pre.push(cur);return pre;}}, []);console.log(res);

3. 统计元素出现的次数

// 输出: { Alice: 2, Bob: 1, Tiff: 1, Bruce: 1 }

  const names = ["Alice", "Bob", "Tiff", "Bruce", "Alice"];let res = names.reduce((pre, cur) => {if (pre[cur]) {pre[cur]++;} else {pre[cur] = 1;}return pre;}, {});console.log(res);

4. 数组扁平化

 const data = [1, 2, [3, 4, [5, 6, 7]], 8, 9, [10, 11]];const myFlat = (arr) => {return arr.reduce((pre, cur) => {return pre.contact(Array.isArray(cur) ? myFlat(cur) : cur);}, []);};console.log(res);

5. 分组

在这里插入图片描述

  const people = [{ name: "Alice", age: 21 },{ name: "Max", age: 20 },{ name: "Jane", age: 20 },];let res = people.reduce((pre, cur) => {if (!pre[cur.age]) {pre[cur.age] = [];}pre[cur.age].push(cur);return pre;}, {});console.log(res);