function groupArrayOfObjects(list, key) {

  return list.reduce(function(rv, x) {

    (rv[x[key]] = rv[x[key]] || []).push(x);

    return rv;

  }, {});

};

​

var people = [

    {sex:"Male", name:"Jeff"},

    {sex:"Female", name:"Megan"},

    {sex:"Male", name:"Taylor"},

    {sex:"Female", name:"Madison"}

];

var groupedPeople=groupArrayOfObjects(people,"sex");

console.log(groupedPeople.Male);//will be the Males 

console.log(groupedPeople.Female);//will be the Females

const groupBy = (arr, groupFn) =>

  arr.reduce(

    (grouped, obj) => ({

      ...grouped,

      [groupFn(obj)]: [...(grouped[groupFn(obj)] || []), obj],

    }),

    {}

  );

const people = [

  { name: 'Matt' },

  { name: 'Sam' },

  { name: 'John' },

  { name: 'Mac' },

];

const groupedByNameLength = groupBy(people, (person) => person.name.length);

/**

{

  '3': [ { name: 'Sam' }, { name: 'Mac' } ],

  '4': [ { name: 'Matt' }, { name: 'John' } ]

}

 */

console.log(groupedByNameLength);

const groupBy = (array, key) => {

  // Return the end result

  return array.reduce((result, currentValue) => {

    // If an array already present for key, push it to the array. Else create an array and push the object

    (result[currentValue[key]] = result[currentValue[key]] || []).push(

      currentValue

    );

    // Return the current iteration `result` value, this will be taken as next iteration `result` value and accumulate

    return result;

  }, {}); // empty object is the initial value for result object

};