假设我们有如下的数组对象：

const users = [
  {
    name: 'Alice',
    age: 25,
    gender: 'female'
  },
  {
    name: 'Bob',
    age: 30,
    gender: 'male'
  },
  {
    name: 'Charlie',
    age: 35,
    gender: 'male'
  },
  {
    name: 'David',
    age: 40,
    gender: 'male'
  },
  {
    name: 'Emily',
    age: 45,
    gender: 'female'
  }
];

我们希望将这个数组按 gender 分组，得到以下格式的新数组：

[
  {
    gender: 'female',
    users: [
      {
        name: 'Alice',
        age: 25,
        gender: 'female'
      },
      {
        name: 'Emily',
        age: 45,
        gender: 'female'
      }
    ]
  },
  {
    gender: 'male',
    users: [
      {
        name: 'Bob',
        age: 30,
        gender: 'male'
      },
      {
        name: 'Charlie',
        age: 35,
        gender: 'male'
      },
      {
        name: 'David',
        age: 40,
        gender: 'male'
      }
    ]
  }
]

我们可以利用 reduce 方法和Object.values()方法来实现：

const groupBy = (list, key) => {
  return list.reduce((result, currentValue) => {
    (result[currentValue[key]] = result[currentValue[key]] || { gender: currentValue[key], users: [] })
      .users.push(currentValue);
    return result;
  }, {});
};

const groupedUsers = Object.values(groupBy(users, 'gender'));

console.log(groupedUsers);

输出结果为：

[
  {
    "gender": "female",
    "users": [
      {
        "name": "Alice",
        "age": 25,
        "gender": "female"
      },
      {
        "name": "Emily",
        "age": 45,
        "gender": "female"
      }
    ]
  },
  {
    "gender