How to merge an arrays of objects js

Question

everyone! I'm doing the project right now and I need some help with the following problem: I have to merge 2 arrays of objects:

1. an array, where each object contains a user id
2. an array, where each object contains information about a user

How can i merge them? I need to compare ids in each object in both arrays and if ids match I need to push the object fron the second array into the object from the first array. So as a result, I need 1 array of objects, where each object contains in itself information about a user from the second object.

an object from a first array looks something like this:

 {
1. country_id: null
2. created_at: "2020-11-13T04:30:16.000000Z"
3. id: 1
4. updated_at: "2020-11-13T04:30:16.000000Z"
}

an object from second array looks like this:

{ 
1. country_id: null
2. created_at: "2020-11-13T04:30:16.000000Z"
3. id: 1
4. name: "1111"
5. photo: null
6. surname: "111"
7. updated_at: "2020-11-13T04:30:16.000000Z"
}

Can anyone help me solve this, please?

Answer 1

Pretty simple if you use ES2018

const resultArray = arr1.map(t1 => ({...t1, ...arr2.find(t2 => t2.id === t1.id)}))

Answer 2

You can convert one array into an object and then iterate over the other to combine both. This way you can have O(n) time complexity.

const arr1 = [
    {
        "country_id": null,
        "created_at": "2020-11-13T04:30:16.000000Z",
        "id": 1,
        "updated_at": "2020-11-13T04:30:16.000000Z"
    }
];
const arr2 = [
    {
        "country_id": null,
        "created_at": "2020-11-13T04:30:16.000000Z",
        "id": 1,
        "name": "1111",
        "photo": null,
        "surname": "111",
        "updated_at": "2020-11-13T04:30:16.000000Z"
    }
];
const dictionary = arr2.reduce((acc, curr) => ({
    ...acc,
    ...(curr.id && { [curr.id]: curr })
}), {});

const mappedArray = arr1
    .map(itemFromFirst => ({ 
        ...itemFromFirst, ...dictionary[itemFromFirst.id] 
    })
);

/* Result:
[{
  "country_id": null,
  "created_at": "2020-11-13T04:30:16.000000Z",
  "id": 1,
  "updated_at": "2020-11-13T04:30:16.000000Z",
  "name": "1111",
  "photo": null,
  "surname": "111"
}] 
*/

Answer 3

Run a loop over first array, picking id for each object.

Then filter the second array based on id; use object spreader to merge the objects.

function mergeOnId(array1, array2) {
  // assuming both the array contain only one object with same id, each.
  var out = []
  for(let i = 0; i < array1.length; i++) {
    for(let j = 0; j < array2.length; j++) {
      if(array1[i].id === array2[j].id) {
        out.push({ ...array1[i], ...array2[j] })
        break;
       }
    }
  }
  return out
}