Filter array of object in javascript

Question

I am creating a project using JavaScript. I am stuck in the problem while filtering the array of object: Here is the array:

var arr1 = [{
      "name": "harkaran",
      "lname": "sofat",
      "userId": 49,
     "postedUserId": 52,
      "id": 21,

    },{
      "name": "harkaran",
      "lname": "sofat",
      "userId": 49,
      "postedUserId": 57,
      "id": 21,
    }]

final array should look like:

[{
    "name": "harkaran",
      "lname": "sofat",
      "userId": 49,
     "postedUserId": 52,
      "id": 21,
      postedUsers:[52,57]
}]

I am trying to creating new object. Here is the approach i am using.But dont know how can i achieve this var arr =[] let obj = {}

        obj['name'] = "";
        obj['lname'] = "";
        obj['userId'] = "";
        obj['postedUserId'] = "";
        obj['id'] = "";
        obj['postedUsers'] = [];
        arr.push(obj);

        for(var i=0; i<arr1.length; i++){


         }

So the first one stays, and the first *and* all the rest go into the array? — Jack Bashford, Jun 09 '19 at 07:23
*"...I want using for loop..."*: if you have such requirements, please make sure to put that in the question, including the reason why. Not everyone reads these comments. — trincot, Jun 09 '19 at 07:43
I thinking, you don`t writing specialized function for this structure. You can writing common uselly function for grouping. As this: https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-a-array-of-objects — Zakhar Yakovlev, Jun 09 '19 at 08:03

score 1 · Answer 1 · answered Jun 09 '19 at 07:23

Use reduce:

var arr1 = [{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":52,"id":21,},{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":57,"id":21,}];
const res = Object.values(arr1.reduce((acc, { postedUserId, name, ...rest }) => {
  acc[name] = acc[name] || { name, ...rest, postedUserId, postedUsers: [] };
  acc[name].postedUsers = [].concat(acc[name].postedUsers, postedUserId);
  return acc;
}, {}));
console.log(res);

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

Maheer Ali · Answer 2 · 2019-06-09T07:55:17.763

First of all this is not called filtering. Its called grouping. You can do that in following steps:

First use reduce() on array and set accumulator to an empty object {}
During each iteration get id and postedUserId is separate variable using Destructuring. And use spread operator to get rest of properties.
Then check if is there already an item present of the current id in accumulator.
If its there then push the postedUserId to its postedUsers array.
If that key is not present then set the key(id) on accumulator to an object with postedUsers as empty array.

var arr1 = [{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":52,"id":21,},{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":57,"id":21,}];

const res = arr1.reduce((ac,{id,postedUserId,...rest}) => {
  if(!ac[id]) ac[id] = {id,postedUserId,postedUsers:[],...rest};
  ac[id].postedUsers.push(postedUserId);
  return ac;

},{})

console.log(Object.values(res))

You asked in the comments for simple for loop so here is the version of that.

var arr1 = [{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":52,"id":21,},{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":57,"id":21,}];

let res = {};

for(let i = 0; i<arr1.length; i++){
  let {id,postedUserId,...rest} = arr1[i];
  if(!res[id]) res[id] = {id,postedUserId,postedUsers:[],...rest};
  res[id].postedUsers.push(postedUserId);
}

console.log(Object.values(res))

@CodeManiac You are right but I consider OP had put that mistakenly. Because there is no point to have `postedUserId` when there is an array of `postedUsers` — Maheer Ali, Jun 09 '19 at 07:41
that's clearly mentioned by OP in comments so i pointed out [Ref](https://stackoverflow.com/questions/56512709/filter-array-of-object-in-javascript/56512807#comment99611827_56512709) — Code Maniac, Jun 09 '19 at 07:43

Code Maniac · Answer 3 · 2019-06-09T07:48:59.507

You can use reduce and group the postedUser and keep the first postedUserId

First loop through arr1 array and use id as key on object we are building
First we check for the id if the object already has value, than check for postedUserId if it's not there add the current id else don't
Now push the postedUserId in postedUser
Get the values from final in the end

var arr1 = [{"name": "harkaran","lname": "sofat","userId": 49,"postedUserId": 52,"id": 21,}, {"name": "harkaran","lname": "sofat","userId": 49,"postedUserId": 57,"id": 21,}]

let final = arr1.reduce((op,{id,...rest})=>{
  let postedUserId = rest.postedUserId
  if(op[id] && op[id].postedUserId){
    delete rest.postedUserId
  }
  op[id] = op[id] || {...rest,postedUser:[]}
  op[id].postedUser.push(postedUserId)
  return op
},{})

console.log(Object.values(final))

score 0 · Answer 4 · answered Jun 09 '19 at 07:53

I would use a temporary Map for the grouping you want.

var arr1 = [{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":52,"id":21,},{"name":"harkaran","lname":"sofat","userId":49,"postedUserId":57,"id":21,}];

const map = new Map(arr1.map(o => [o.id, { ...o, postUsersId: [] }]));
arr1.forEach(o => map.get(o.id).postUsersId.push(o.postedUserId));
const res = [...map.values()];

console.log(res);

This will give precedence to the data given with the last occurrence of the same id. If you want the first to have precedence, then just reverse the array

Filter array of object in javascript

4 Answers4