How to group or merge this array of objects in javascript?

Question

I have an array of objects like below for example.

{name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0}
{name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0}
{name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0}
{name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1}
{name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1}
{name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0}
{name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1}
{name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1}

I want to group them up and adding up all the values in it. For example, the final would be like this:

{name: "Mc Donald", quantity: 8, maleCount: 1, femaleCount: 1}
{name: "KFC", quantity: 54, maleCount: 3, femaleCount: 3}

How can I achieve this in JavaScript?

I have tried to find some solution online but it is not the one I wanted. For example this solution

score 15 · Accepted Answer · answered Oct 10 '17 at 10:21

You can use array reduce:

var arr = [
    {name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0},
    {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
    {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
    {name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1},
    {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
    {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
    {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
    {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1}
];

var finalArr = arr.reduce((m, o) => {
    var found = m.find(p => p.name === o.name);
    if (found) {
        found.quantity += o.quantity;
        found.maleCount += o.maleCount;
        found.femaleCount += o.femaleCount;
    } else {
        m.push(o);
    }
    return m;
}, []);

console.log(finalArr);

Just noting that this solution will modify some of the original objects. — Prestaul, Oct 10 '17 at 22:30

Nenad Vracar · Answer 2 · 2017-10-10T13:05:56.007

You can use forEach() loop and add to new array. You can pass empty object as thisArg parameter that you can use as this in your callback function and in second forEach context of this will still be the same as in first callback function because of arrow function.

var data = [{"name":"Mc Donald","quantity":4,"maleCount":1,"femaleCount":0},{"name":"KFC","quantity":9,"maleCount":1,"femaleCount":0},{"name":"KFC","quantity":9,"maleCount":1,"femaleCount":0},{"name":"Mc Donald","quantity":4,"maleCount":0,"femaleCount":1},{"name":"KFC","quantity":9,"maleCount":0,"femaleCount":1},{"name":"KFC","quantity":9,"maleCount":1,"femaleCount":0},{"name":"KFC","quantity":9,"maleCount":0,"femaleCount":1},{"name":"KFC","quantity":9,"maleCount":0,"femaleCount":1}]
var result = [], keys = ['quantity', 'maleCount', 'femaleCount']

data.forEach(function(e) {
  if(!this[e.name]) result.push(this[e.name] = e);
  else keys.forEach(k => this[e.name][k] += e[k])
}, {})

console.log(result)

Using `this` like that needs some more explanation, please. – Bergi Oct 10 '17 at 12:52 — Bergi, Oct 10 '17 at 12:52

Nina Scholz · Answer 3 · 2017-10-10T11:10:58.843

You could group with a hash table and use an array for the keys with variable values.

var array = [{ name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0 }, { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 }, { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 }, { name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1 }, { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 }, { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 }, { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 }, { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 }],
    groups = Object.create(null),
    result = array.reduce(function (r, o) {
        var values = ['quantity', 'maleCount', 'femaleCount'];
        if (!groups[o.name]) {
            groups[o.name] = { name: o.name };
            r.push(groups[o.name]);
            values.forEach(function (k) { groups[o.name][k] = 0; });
        }
        values.forEach(function (k) { groups[o.name][k] += o[k]; });
        return r;
    }, []);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

With linq.js

var array = [{ name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0 }, { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 }, { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 }, { name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1 }, { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 }, { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 }, { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 }, { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 }],
    result = Enumerable.From(array)
        .GroupBy(
            "$.name",
            null,
            "{ name: $.Key, quantity: $$.Sum('$.quantity'), maleCount: $$.Sum('$.maleCount'), femaleCount: $$.Sum('$.femaleCount') }"
        )
        .ToArray();

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/linq.js/2.2.0.2/linq.js"></script>

Is there a reason to do `groups = Object.create(null)` instead of simply `groups = {}`? — Rick Hitchcock, Oct 10 '17 at 14:52
if you have a name like `toString`, you could get wrong results with prototypes. — Nina Scholz, Oct 10 '17 at 14:54

score 2 · Answer 4 · answered Oct 10 '17 at 12:29

My solution based on reduce:

let data = [
  {name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0},
  {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
  {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
  {name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1},
  {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
  {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
  {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
  {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1}
];

// We will only keep an array of values of the merged object
let result = Object.values(
  // Merge data to name indexed objects
  data.reduce((p,c) => {
    // Ensure key (name) exists
    if (!p[c.name]) {
       // If first occurence, duplicate object (to avoid modification of original array)
       p[c.name] = Object.assign({}, c);
    } else {
       // If key (name) already exists, sum up relevant attributes
       p[c.name].quantity += c.quantity;
       p[c.name].maleCount += c.maleCount;
       p[c.name].femaleCount += c.femaleCount;
    }
    // return updated object
    return p;
  }, {})
);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

hope this will help

score 1 · Answer 5 · answered Oct 10 '17 at 10:28

More functional/universal approach

const normalizeValue = (value) => value === undefined ? 0 : value
const sumUpProps = (props = []) => (a = {}, b = {}) => {
  const result = {}
  
  props.forEach((prop) => {
    result[prop] = normalizeValue(a[prop]) + normalizeValue(b[prop])
  })

  return result
}

const data = [
  {name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0},
  {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
  {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
  {name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1},
  {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
  {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
  {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
  {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1}
]

const entries = {}
const sumObjects = sumUpProps(['quantity', 'maleCount', 'femaleCount'])

data.forEach((item) => {
  const entry = entries[item.name] || {}

  entries[item.name] = sumObjects(entry, item)
})


console.log(entries)

score 1 · Answer 6 · answered Oct 10 '17 at 10:33

check this code below:

var array = [
    {name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0},
    {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
    {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
    {name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1},
    {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
    {name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0},
    {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
    {name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1},
];

var result = [];

for(var index in array){
    var obj = array[index];
    if(result.hasOwnProperty(obj.name)) {
        result[obj.name].quantity += obj.quantity;
        result[obj.name].maleCount += obj.maleCount;
        result[obj.name].femaleCount += obj.femaleCount;
    }else{
        result[obj.name] = {};
        result[obj.name].quantity = obj.quantity;
        result[obj.name].maleCount = obj.maleCount;
        result[obj.name].femaleCount = obj.femaleCount;
    }
}

console.log(result);

score 1 · Answer 7 · answered Oct 10 '17 at 12:09

Here is a generic solution that uses clean and modern JavaScript:

function groupRestaurants(restaurants) {
    const groups = new Map();
    restaurants.forEach(restaurant => {
        const group = findOrCreateGroup(groups, restaurant.name);
        addRestaurantToGroup(group, restaurant);
    });
    return [...groups.values()];
}

function findOrCreateGroup(groups, name) {
    let group = groups.get(name);
    if (!group) {
        group = { name };
        groups.set(name, group);
    }
    return group;
}

function addRestaurantToGroup(group, restaurant) {
    for (const [key, value] of Object.entries(restaurant)) {
        if (key !== 'name') {
            if (group.hasOwnProperty(key)) {
                group[key] += value;
            } else {
                group[key] = value;
            }
        }
    }
}

const restaurants = [
    { name: "Mc Donald", quantity: 4, maleCount: 1, femaleCount: 0 },
    { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 },
    { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 },
    { name: "Mc Donald", quantity: 4, maleCount: 0, femaleCount: 1 },
    { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 },
    { name: "KFC", quantity: 9, maleCount: 1, femaleCount: 0 },
    { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 },
    { name: "KFC", quantity: 9, maleCount: 0, femaleCount: 1 }
];

console.log(groupRestaurants(restaurants));

score 1 · Answer 8 · answered Oct 10 '17 at 15:46

Lodash makes your life easy.

_.map(_.groupBy(yourArrayHere, 'name'), (groupMembers, groupKey) => {
    let sumObject = {name: groupKey};

    _.forEach(['quantity', 'maleCount', 'femaleCount'], (property) => {
        sumObject[property] = 0;
        _.forEach(groupMembers, (member) => {
            sumObject[property] += member[property];
        });
    });

    return sumObject;
});

How to group or merge this array of objects in javascript?

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