How to group by and sum an array of objects?

Question

I would like to group an array of objects by Id and sum the quantity in jQuery. How can I achieve this?

For example:

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

Should result in:

[
  { Id: "001", qty: 3 },
  { Id: "002", qty: 2 },
  { Id: "003", qty: 4 }
]

Answer 1

You can loop and sum it up (reduce documentation)

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)

Fiddle: Fiddle