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 }
]

An updated, TypeScript-friendly SO that also supports multiple grouping keys is discussed [here](https://stackoverflow.com/a/76272302/8929855) — swimmer, May 23 '23 at 17:10

score 117 · Accepted Answer · edited Dec 09 '22 at 10:43

117

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

edited Dec 09 '22 at 10:43

live2

3,771
2
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46

answered Mar 31 '15 at 08:51

Arun P Johny

384,651
66
527
531

2

setting `qty` to 0 is important in the `res[value.Id] = { qty: 0, Id: value.Id};` step. Otherwise u get duplicate values – JustLearning May 03 '17 at 08:53
9

Should this not be var result = array.reduce.... instead of using a sideeffect? – mplungjan Jan 02 '19 at 10:39

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

1

var newArr = [];

$.each(array,function(index,element){
    if(newArr[element.Id]==undefined){
        newArr[element.Id] =0;
    }
    newArr[element.Id] += element.qty;
});
console.log(newArr);

Demo

edited Jun 20 '20 at 09:12

Community

1
1

answered Mar 31 '15 at 08:54

Sadikhasan

18,365
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122

You are not creating an array of objects – mplungjan Jan 02 '19 at 10:19
This uses element.id as an array index, not as an object key. – treecon Dec 19 '20 at 10:56

How to group by and sum an array of objects?

2 Answers2

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