使用lodash进行分组和分层映射

const _ = require('lodash');

const users = [
  { name: 'Alice', age: 25, city: 'New York' },
  { name: 'Bob', age: 30, city: 'New York' },
  { name: 'Charlie', age: 28, city: 'Los Angeles' },
  { name: 'David', age: 35, city: 'Los Angeles' },
];

// 根据城市分组
const groupedByCity = _.groupBy(users, 'city');
console.log(groupedByCity);

// 统计每个城市的用户数量
const cityUserCount = _.mapValues(groupedByCity, (usersInCity) => usersInCity.length);
console.log(cityUserCount);

// 确保每个用户对象都有 'city' 键
const users = [
  { name: 'Alice', age: 25, city: 'New York' },
  { name: 'Bob', age: 30, city: 'New York' },
  { name: 'Charlie', age: 28, city: 'Los Angeles' },
  { name: 'David', age: 35, city: 'Los Angeles' },
];

// 确保映射函数逻辑正确
const cityUserCount = _.mapValues(groupedByCity, (usersInCity) => usersInCity.length);