merge duplicate objects in an array and add additional property

Question

i have a problem, with my code basically i'm trying to merge the duplicate objects and add the additional property 'admin' set to 'true' and for unique objects additional property 'admin' set to 'false'

const addresses = [{name: 'Paul', id: 2}, {name: 'John', id: 1}, {name: 'John', id: 1}];

//combine duplicate object and add property admin: true

let result = [];
addresses.forEach(elem => {
  let match = result.find(r => r.id === elem.id);
  if(match) {
    return {...match, ...elem, admin: true};
  } else {
    result.push({...elem, admin: false });
  }
});

but im doing this incorrectly as the output i get is

const addresses = [{name: 'Paul', id: 2}, {name: 'John', id: 1}, {name: 'John', id: 1}];

You are modifying `result` not the original array. Note that `return` in `forEach` does nothing — charlietfl, Jul 20 '19 at 11:48
Does this answer your question? [Merge duplicate objects in array of objects](https://stackoverflow.com/questions/30025965/merge-duplicate-objects-in-array-of-objects) — leonheess, May 09 '22 at 20:30

User863 · Answer 1 · 2019-07-20T11:57:22.977

2

Using reduce()

const addresses = [{name: 'Paul', id: 2}, {name: 'John', id: 1}, {name: 'John', id: 1}];

const result = addresses.reduce((a, o) => ({...a, ...{
  [o.id]: { ...o, admin: !a[o.id] }
}}), {});

console.log(Object.values(result));

edited Jul 20 '19 at 11:57

answered Jul 20 '19 at 11:52

User863

19,346
2
17
41

score 2 · Accepted Answer · answered Jul 20 '19 at 11:58

You can use reduce to create a unique array that sets admin property to true for duplicate addresses as follows:

const addresses = [{name: 'Paul', id: 2}, {name: 'John', id: 1}, {name: 'John', id: 1}];

const result = addresses.reduce((acc, address) => {
  const dup = acc.find(addr => addr.id === address.id);
  if (dup) {
    dup.admin = true;
    return acc;
  }
  address.admin = false;
  return acc.concat(address);
}, [])

console.log(result);

Hassan Imam · Answer 3 · 2019-07-20T12:07:13.543

0

You can use array#reduce to group the unique addresses and then check for admin property in the object and accordingly assign the value.

const addresses = [{name: 'Paul', id: 2}, {name: 'John', id: 1}, {name: 'John', id: 1}],
      users = Object.values(addresses.reduce((r,o) => {
        r[o.id] = {...o, admin: !r[o.id]};
        return r;
      }, {}));
console.log(users);

edited Jul 20 '19 at 12:07

answered Jul 20 '19 at 11:51

Hassan Imam

21,956
5
41
51

merge duplicate objects in an array and add additional property

3 Answers3