LoDash Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.9.0/lodash.min.js"></script>

JavaScript

// loaded from API Request into array
var OnlineList = [];
//  Sorted and ordered for display
var OnlineUsers = [];
OnlineList = [
  {
    "Role": "Adjuster",
    "AccountId": "4",
    "UserId": "1e72d58e",
    "DisplayName": "Big Bob",
  },
  {
    "Role": "Adviser",
    "AccountId": "5",
    "UserId": "a0daba73",
    "DisplayName": "Sassy Sally",
  }
];

// GroupBy function: https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects/43215522
let groupBy = function(xs, key) {
	return xs.reduce(function(rv, x) {
      (rv[x[key]] = rv[x[key]] || []).push(x);
      return rv;
  }, {});
};

// Simulates a get by Id API service
let accountService = (id) => {
	if (id == 4) {
  return "ClaimsCo."
  }
 	else  {
  return "Dealership"
  }
}

// pass in AccountId
let getAccountName = function(int) {
  var accountName = "";
  //get AccountName from Id
  accountName = accountService(int);
    for(var x=0; x < OnlineList.length; x++){
    // check for AccountId
      if(OnlineList[x].hasOwnProperty('AccountId')){
      // Set AccountId value to AccountName
      OnlineList[x].AccountId = accountName;
      // Group results and set to OnlineUsers array
      OnlineUsers = groupBy(OnlineList, 'AccountId');
      break;
     }
	}
};

// Go into first element of array and get AccountId value
var id = _.get(OnlineList[0], "AccountId");
// Convert value to int
var int = parseInt(id,10);
// Pass into function that gets AccountName from AccountId and replaces AccountId in that element of OnlineList array
getAccountName(int);

//result
console.log(OnlineUsers);