现代JavaScript_Array分组方法

const users = [
  { name: 'Alice', gender: 'female' },
  { name: 'Bob',   gender: 'male' },
  { name: 'Charlie', gender: 'male' },
  { name: 'Diana', gender: 'female' }
];

const grouped = users.reduce((acc, item) => {
  const key = item.gender;
  if (!acc[key]) acc[key] = [];
  acc[key].push(item);
  return acc;
}, {});

// 结果：
// {
//   female: [ {name: 'Alice', ...}, {name: 'Diana', ...} ],
//   male: [ {name: 'Bob', ...}, {name: 'Charlie', ...} ]
// }

const people = [
  { name: 'Tom', age: 25 },
  { name: 'Jerry', age: 34 },
  { name: 'Lucy', age: 19 },
  { name: 'John', age: 36 }
];

const groupByAgeRange = people.reduce((map, person) => {
  const range = person.age < 30 ? 'under-30' : '30-and-over';
  if (!map.has(range)) map.set(range, []);
  map.get(range).push(person);
  return map;
}, new Map());

// 转为对象（可选）
Object.fromEntries(groupByAgeRange);

function groupBy(array, keyFn) {
  return array.reduce((acc, item) => {
    const key = keyFn(item);
    if (!acc[key]) acc[key] = [];
    acc[key].push(item);
    return acc;
  }, {});
}

// 使用方式
const groupedByGender = groupBy(users, user => user.gender);
const groupedByInitial = groupBy(users, user => user.name[0].toUpperCase());

// 注意：目前不建议生产环境使用
const grouped = Object.groupBy(users, user => user.gender);