array group by reduce javascript code example

Example 1: javascript group by property array of objects

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

Example 2: javascript group by sum array reduce

var array = [
  { Id: "001", qty: 1 }, 
  { Id: "002", qty: 2 }, 
  { Id: "001", qty: 2 }, 
  { Id: "003", qty: 4 }
];

var result = [];
array.reduce(function(res, value) {
  if (!res[value.Id]) {
    res[value.Id] = { Id: value.Id, qty: 0 };
    result.push(res[value.Id])
  }
  res[value.Id].qty += value.qty;
  return res;
}, {});

console.log(result)