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++){


         }

Answer 1

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; } 

Answer 2

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)) 

Answer 3

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)) 

Answer 4

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