使用 lodash/Javascript 对班级进行分组并统计用户

Question

得到一个数组列表，其中包含参加过的课程和用户的列表；需要一个输出，通过对课程分组并计算总用户数来显示参加过的用户；

var arrList = [
  { class: 'one', user: 'user1' },
  { class: 'two', user: 'user1' },
  { class: 'two', user: 'user2' },
  { class: 'one', user: 'user3' },
  { class: 'two', user: 'user3' },
  { class: 'three', user: 'user1' },
  { class: 'four', user: 'user1' }
];

// output
[
  { class: 'one', user: [ 'user1', 'user2', 'user3' ], count: 3 },
  { class: 'two', user: [ 'user1', 'user3' ], count: 2 },
  { class: 'three', user: [ 'user1' ], count: 1 },
  { class: 'four', user: [ 'user1' ], count: 1 } 
];

Answer 1

使用_.groupBy()通过class键收集对象，然后映射到需要的形式。

链式解决方案（需要完全导入 lodash 包）：

const arrList = [{"class":"one","user":"user1"},{"class":"two","user":"user1"},{"class":"two","user":"user2"},{"class":"one","user":"user3"},{"class":"two","user":"user3"},{"class":"three","user":"user1"},{"class":"four","user":"user1"}];

const result = _(arrList)
  .groupBy('class')
  .map((group, key) => ({
    class: key,
    user: _.map(group, 'user'),
    count: group.length
  }))
  .value();
  
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script>

使用_.flow() 的解决方案（可以从 lodash 包中导入您需要的内容）：

const { flow, partialRight: pr, groupBy, map } = _; // replace with imports in your project

const fn = flow(
  pr(groupBy, 'class'),
  pr(map, (group, key) => ({
    class: key,
    user: map(group, 'user'),
    count: group.length
  }))
);
  
const arrList = [{"class":"one","user":"user1"},{"class":"two","user":"user1"},{"class":"two","user":"user2"},{"class":"one","user":"user3"},{"class":"two","user":"user3"},{"class":"three","user":"user1"},{"class":"four","user":"user1"}];

const result = fn(arrList);
  
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script>