concat same id within object to one array of object

Question

I have data which is structured like this:

let siteLists = [
    {
        "data": {
            "client_id": 29
        },
        "all_branch": 1,
        "value": 29,
        "label": "A Site"
    },
    {
        "data": {
            "client_id": 23,
        },
        "all_branch": 0,
        "value": 91,
        "label": "B-1 Site"
    },
    {
        "data": {
            "client_id": 23,
        },
        "all_branch": 0,
        "value": 86,
        "label": "B-2 Site"
    },
    {
        "data": {
            "client_id": 10
        },
        "all_branch": 1,
        "value": 10,
        "label": "C Site"
    }
];

I need to concatenate the above object which has same data.client_id value into one object which contains all branch values.

Expected result:

[
  {
    id: 29, 
    branches: [],
    all_branch:1
  },
  {
    id: 23, 
    branches: [91,86],
    all_branch:0
  },
  {
    id: 10,
    branches: [],
    all_branch:1
  }
]

I tried the following code but the result did not fit the expected result...

let populate = [...siteLists.map(item => {
  return item.all_branch === 1 ? {
    all_placement: 1,
    placement_id: item.data.client_id,
    branch_id: []
  } : {
    all_placement: 0,
    placement_id: item.data.client_id,
    branch_id: [item.value]
  }
})];

Answer 1

This should work, may not be optimal though. I also took the liberty to add the values to branches array instead of leaving it empty.

let siteLists = [{
    "data": {
      "client_id": 29
    },
    "all_branch": 1,
    "value": 29,
    "label": "A Site"
  },
  {
    "data": {
      "client_id": 23,
    },
    "all_branch": 0,
    "value": 91,
    "label": "B-1 Site"
  },
  {
    "data": {
      "client_id": 23,
    },
    "all_branch": 0,
    "value": 86,
    "label": "B-2 Site"
  },
  {
    "data": {
      "client_id": 10
    },
    "all_branch": 1,
    "value": 10,
    "label": "C Site"
  }
];
var resultarray = []; //expected result
var branchId = []; //stores an object to map the branch ID and the array index to keep track of duplicate IDs
var count = 0; //keeps track of the current array Index
siteLists.forEach(element => { //for loop to loop through siteList array
  var resultObj = new Object(); //stores the temporary result Object
  var id = element.data.client_id;
  var status = false; //keeps track of if it is a duplicate ID
  if (count != 0) {
    branchId.forEach(obj => { //for loop to check for duplicate ID (will only run after the first iteration of result loop)
      if (obj.id === id) { //checks if the ID matches
        var index = obj.index;
        var value = element.value;
        resultarray[index].branches.push(obj.value);//pushes the matched ID value
        resultarray[index].branches.push(value); //Pushes value to branches array if ID is duplicate
        status = true;
      }
    })
  }
  if (status == false) {
    var branchObj = {
      'id': id,
      'index': count,
      'value':element.value
    }
    var allBranch = element.all_branch;
    //var value = element.value; //uncomment if you need value in the resultObj when id does not match
    branchId.push(branchObj);
    resultObj.id = id;
    resultObj.branches = [];
    //resultObj.branches.push(value);//uncomment if you need value in the resultObj when id does not match
    resultObj.all_branch = allBranch;
    resultarray.push(resultObj);
    count = count + 1;
  } else {
    status = false;
  }

})
console.log(resultarray);