Group array of objects by id in javascript

Question

There are three objects like this.

var Object1 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "nickname": "uknowTest2",
        "createdAt": "2022-03-22T07:50:41.769Z",
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "nickname": "qnvvzjrh",
        "createdAt": "2022-03-21T07:10:04.888Z",
        "animalCount": 1
    }
];

var Object2 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "data": 36
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "data": 542717
    }
];

var Object3 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "data2": 133111
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "data2": 540517
    }
];

And I want to group them like this:

var result = [
    {   
        "_id": "62397fd1c517e11e05935cc7",
        "data": 36,
        "data2": 133111,
        "nickname": "uknowTest2",
        "createdAt": "2022-03-22T07:50:41.769Z",
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "data": 542717,
        "data2": 540517,
        "nickname": "qnvvzjrh",
        "createdAt": "2022-03-21T07:10:04.888Z",
        "animalCount": 1
    }
];

Several similar types of data are generated. I'm not sure what to do. Using object.assign doesn't seem to be the solution.

Suman Majhi · Accepted Answer · 2022-03-23 06:33:32Z

4

This solution is taking time complexity of O(n)

Here you go:

const allObj = [...Object1, ...Object2, ...Object3];

const preResult = {};
allObj.forEach((obj)=> {
    preResult[obj._id] = preResult[obj._id] ? {...preResult[obj._id], ...obj} : obj;
})

const result = Object.values(preResult)
console.log(result)

Explaination:

allObj is the concatenation of all objects
allObj.forEach is looping through all elements (sub objects)
Using ternary operator to assign the value
If obj._id (key) already exist in preResult, then assign {...preResult[obj._id], ...obj} (which is concat of existed value and new value)
Else assign new value obj
preResult is pair of obj._id (key) and merged-object (values)
final result is the only values of preResult

Code Snippet:

var Object1 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "nickname": "uknowTest2",
        "createdAt": "2022-03-22T07:50:41.769Z",
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "nickname": "qnvvzjrh",
        "createdAt": "2022-03-21T07:10:04.888Z",
        "animalCount": 1
    }
];

var Object2 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "data": 36
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "data": 542717
    }
];

var Object3 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "data2": 133111
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "data2": 540517
    }
];

const allObj = [...Object1, ...Object2, ...Object3];

const preResult = {};
allObj.forEach((obj)=> {
    preResult[obj._id] = preResult[obj._id] ? {...preResult[obj._id], ...obj} : obj;
})

// console.log(preResult)

const result = Object.values(preResult)

console.log(result)

edited Mar 23, 2022 at 6:33

answered Mar 23, 2022 at 6:05

Suman Majhi

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5 Comments

Hritik Sharma Over a year ago

Definitely, this is a very optimised solution.

k. kh Over a year ago

Received fairly high quality answers. thank you.

Suman Majhi Over a year ago

@Nikkkshit 1. allObj is the concatenation of all objects 2. allObj.forEach is looping through all elements (sub objects) 3. Using ternary operator to assign the value 4. If obj._id already exist in preResult, then assign {...preResult[obj._id], ...obj} (Concat of pre value and new value) 5. Else assign new value obj 6. preResult is pair of obj._id and values 7. final result is the only values of preResult

Rickard Elimää Over a year ago

@SumanMajhi Please edit your post, and explain your code there, instead of explaining in the comments.

Suman Majhi Over a year ago

@RickardElimää done

Hritik Sharma · Accepted Answer · 2022-03-23 06:00:35Z

var Object1 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "nickname": "uknowTest2",
        "createdAt": "2022-03-22T07:50:41.769Z",
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "nickname": "qnvvzjrh",
        "createdAt": "2022-03-21T07:10:04.888Z",
        "animalCount": 1
    }
];

var Object2 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "data": 36
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "data": 542717
    }
];

var Object3 = [
    {
        "_id": "62397fd1c517e11e05935cc7",
        "data2": 133111
    },
    {
        "_id": "623824ccd1164bb8d9cc2521",
        "data2": 540517
    }
];
let result = [...Object1];

let temp = [...result];
Object2.map(val=>{
  result.map((val2,index)=>{
    if(val2._id===val._id){
      val2 = {...val2,...val};
      temp[index] = val2
    }
  })
})
result = [...temp];
Object3.map(val=>{
  result.map((val2,index)=>{
    if(val2._id===val._id){
      val2 = {...val2,...val};
      temp[index] = val2
    }
  })
})
console.log(temp)

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