How to group by and sum an array of objects? [duplicate]

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 — swimmer
– swimmer, Commented May 23, 2023 at 17:10

live2 · Accepted Answer · 2022-12-09 10:43:06Z

125

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 9, 2022 at 10:43

live2

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answered Mar 31, 2015 at 8:51

Arun P Johny

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3 Comments

JustLearning Over a year ago

setting qty to 0 is important in the res[value.Id] = { qty: 0, Id: value.Id}; step. Otherwise u get duplicate values

mplungjan Over a year ago

Should this not be var result = array.reduce.... instead of using a sideeffect?

Ari Waisberg Over a year ago

I believe this only work because the Id is numeric cause the Index of the array cannot be a string...

Community · Accepted Answer · 2020-06-20 09:12:55Z

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, 2020 at 9:12

CommunityBot

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answered Mar 31, 2015 at 8:54

Sadikhasan

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2 Comments

mplungjan Over a year ago

You are not creating an array of objects

treecon Over a year ago

This uses element.id as an array index, not as an object key.

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