const group = (

  array, func = v => v, detail = false

) => {

  const index = [];

  const result = [];

  array.forEach(v => {

    const funcResult = func(v);

    const i = index.indexOf(funcResult);

    if (i === -1) {

      index.push(funcResult);

      result.push([v]);

    } else {

      result[i].push(v);

    }

  });

​

  if (detail) {

    return { index, result };

  }

  return result;

};

​

const data = [

  {name: 'aaa', age: 18,},

  {name: 'bbb', age: 20,},

  {name: 'bbb', age: 21,},

  {name: 'ccc', age: 21,},

  {name: 'bbb', age: 20,},

];

​

console.log(

  group(data, d => d.name, {detail: true}),

);

// {

//   index: ['aaa', 'bbb', 'ccc'],

//   result: [

//     [{ name: 'aaa', age: 18 }],

//     [

//       { name: 'bbb', age: 20 },

//       { name: 'bbb', age: 21 },

//       { name: 'bbb', age: 20 },

//     ],

//     [{ name: 'ccc', age: 21 }]

//   ]

// }

​

console.log(

  group(data, d => d.name, {detail: true})

    .result.map(e => ({ name: e[0].name, count: e.length })),

);

// [

//   { name: 'aaa', count: 1 },

//   { name: 'bbb', count: 3 },

//   { name: 'ccc', count: 1 },

// ]

​

console.log(

  group(data, d => d.name + d.age.toString(), {detail: true}),

);

// {

//   index: ['aaa18', 'bbb20', 'bbb21', 'ccc21'],

//   result: [

//     [{ name: 'aaa', age: 18 }],

//     [

//       { name: 'bbb', age: 20 },

//       { name: 'bbb', age: 20 },

//     ],

//     [

//       { name: 'bbb', age: 21 },

//     ],

//     [{ name: 'ccc', age: 21 }],

//   ],

// }

​

console.log(

  group(data, d => d.name + d.age.toString(), {detail: true})

    .result.map(e => ({ name: e[0].name, age: e[0].age, count: e.length })),

);

// [

//   { name: 'aaa', age: 18, count: 1 },

//   { name: 'bbb', age: 20, count: 2 },

//   { name: 'bbb', age: 21, count: 1 },

//   { name: 'ccc', age: 21, count: 1 },

// ],

​