merge duplicate objects in an array and combine sub array of each object

Question

I am trying to merge objects based off of Id, and merge each array that lives inside each account (object), but instead of merging the contents of accountList, the code overwrites the array, if there is a matching id.

I've made a new array and used the .find method to find matching objects based off there id, but stuck on how to merge the accountList together

const accounts = [
    {
    "Id": 103,
    "accountList": [
      {}
    ]
  },
  {
    "Id": 103,
    "accountList": [
      {
        "tokenId": "5aasdasdsdnjn3434nadd",
        "featureId": 2840
      }
    ]
  },
  {
    "Id": 112,
    "accountList": [
      {
        "tokenId": "5d30775bef4a722c38aefaaa",
        "featureId": 2877
      }
    ]
  },
    {
    "Id": 112,
    "accountList": [
      {
        "tokenId": "5d30775bef4a722c38aefccc",
        "featureId": 2856
      }
    ]
  }
]

let result = [];
accounts.forEach(account => {
  let match = result.find(r => r.Id === account.Id);
  // console.log(match)
  if(match) {
   Object.assign(match, account);
    //tried using spread operator instead of object assign, but didnt work
    //  match = {...match, ...account}
  } else {
    result.push(account);
  }
});

console.log( JSON.stringify(result, null, 2))

The result which i need is to merge the object based off their id, and merge the contents of the accountList together, like so:

[
  {
    "Id": 103,
    "accountList": [
      {
        "tokenId": "5aasdasdsdnjn3434nadd",
        "featureId": 2840
      }
    ]
  },
  {
    "Id": 112,
    "accountList": [
      {
        "tokenId": "5d30775bef4a722c38aefaaa",
        "featureId": 2877
      },
      {
        "tokenId": "5d30775bef4a722c38aefccc",
        "featureId": 2856
      }
    ]
  }
]

I updated my code, initially the empty object was also included. This has been fixed now. My bad. — Fullstack Guy, Sep 04 '19 at 10:55
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

Yevhen Horbunkov · Accepted Answer · 2020-07-12T21:33:44.587

I think, reduce() would do the job:

const accounts = [{"Id":103,"accountList":[{}]},{"Id":103,"accountList":[{"tokenId":"5aasdasdsdnjn3434nadd","featureId":2840}]},{"Id":112,"accountList":[{"tokenId":"5d30775bef4a722c38aefaaa","featureId":2877}]},{"Id":112,"accountList":[{"tokenId":"5d30775bef4a722c38aefccc","featureId":2856}]}];

const result = [...accounts
        .reduce((r, o) => {
          const record = r.get(o.Id)||{}
          r.set(o.Id, {
            Id: o.Id,
            accountList: [
              ...(record.accountList||[]),
              ...o.accountList.filter(o => 
                Object.keys(o).length != 0)
            ]            
          })
          return r
        }, new Map())
        .values()]

console.log(result);

.as-console-wrapper {min-height: 100%}

@RakibulIslam : That doesn't seem to be the case according to OP's example. — Yevhen Horbunkov, Aug 30 '19 at 12:15

Fullstack Guy · Answer 2 · 2019-09-04T10:48:44.693

Using Array.prototype.reduce we can accumulate the results in the final result array.

In the reduce call back just find the matching object using Id and merge the accountList array and not the object as you were doing in your code.

const accounts=[{"Id":103,"accountList":[{}]},{"Id":103,"accountList":[{"tokenId":"5aasdasdsdnjn3434nadd","featureId":2840}]},{"Id":112,"accountList":[{"tokenId":"5d30775bef4a722c38aefaaa","featureId":2877}]},{"Id":112,"accountList":[{"tokenId":"5d30775bef4a722c38aefccc","featureId":2856}]}];

const result = accounts.reduce((acc, account) => {
     let match = acc.find(r => r.Id === account.Id);
     if(match) {
       match.accountList.push(...account.accountList); //push previous array
     } else {
       const act = { ...account }; 
       act.accountList = account.accountList.filter((obj) => Object.keys(obj).length);
       acc.push(act);
     }
     return acc;
}, []);
console.log(result);

Alexander Paschenko · Answer 3 · 2019-08-30T11:40:30.030

You can try to use Array.concat:

    let result = [];
    accounts.forEach(account => {
      let match = result.find(r => r.Id === account.Id);
      // console.log(match)
      if(match) {
        match.accountList = match.accountList.concat(account.accountList);
      } else {
        result.push(account);
      }
    });

for (let res of result) {
  console.log('res.Id: ', res.Id, res.accountList)
}

// res.Id:  103 [ {}, { tokenId: '5aasdasdsdnjn3434nadd', featureId: 2840 } ]
// res.Id:  112 [ { tokenId: '5d30775bef4a722c38aefaaa', featureId: 2877 },
//   { tokenId: '5d30775bef4a722c38aefccc', featureId: 2856 } ]

shrys · Answer 4 · 2019-08-30T11:33:02.277

I think you could use match.accountList.push(...account.accountList); instead of the object assign, spread operator can be used to push the element into the result item(match):

let accounts = [{ "Id": 103, "accountList": [{}] }, { "Id": 103, "accountList": [{ "tokenId": "5aasdasdsdnjn3434nadd", "featureId": 2840 }] }, { "Id": 112, "accountList": [{ "tokenId": "5d30775bef4a722c38aefaaa", "featureId": 2877 }] }, { "Id": 112, "accountList": [{ "tokenId": "5d30775bef4a722c38aefccc", "featureId": 2856 }] }];
let result = [];
accounts.forEach(account => {
  (match = result.find(r => r.Id === account.Id), match ? match.accountList.push(...account.accountList) : result.push(account))
});
console.log(result);

Abito Prakash · Answer 5 · 2019-08-30T14:04:06.613

const isNotEmptyObject = objc => Object.entries(objc).length > 0;

function mergeAccounts(accounts) {
    const uniqueAccounts = new Map();
    accounts.forEach(account => {
        if(uniqueAccounts.has(account.Id)) {
            let uniqueAccount = uniqueAccounts.get(account.Id);
            if(account.accountList && account.accountList.length > 0)
                uniqueAccount.accountList.push(...account.accountList);
                uniqueAccount.accountList = uniqueAccount.accountList.filter(isNotEmptyObject);
        } else {
            uniqueAccounts.set(account.Id, account);
        }
    });
  return Array.from(uniqueAccounts.values());
}

This will merge all the accounts having same ids. Hope this helps :)

merge duplicate objects in an array and combine sub array of each object

5 Answers5