ng-option with track by

<!DOCTYPE html>
<html ng-app="plunker">

  <head>
    <meta charset="utf-8" />
    <title>AngularJS Plunker</title>
    <script data-require="angular.js@1.3.x" src="https://code.angularjs.org/1.3.20/angular.js" data-semver="1.3.20"></script>
    <script src="script.js"></script>
  </head>

  <body>
  <div ng-controller="MyCtrl">
   <ul>
     
   <div ng-repeat="data in items">
     <select ng-model="data.selected" 
             ng-options="choice as choice.keyName for choice in data.choices track by choice.keyName"
             ng-change="selection(data.selected)">
       <option value="">Select</option>
     </select>
     
   </div>
   <br>
    <br>
  <div ng-repeat="data in items">
      <select ng-model="data.selected" 
             ng-options="choice as choice.arg for choice in data.choices track by choice.arg"
             ng-change="selection(data.selected)">
       <option value="">Select</option>
     </select>
   </div>
   
   </ul>
</div>
  </body>

</html>

// Code goes here

var myApp = angular.module('plunker',[]);
angular.module('plunker').controller('MyCtrl', MyCtrl)
MyCtrl.$inject = ['$scope'];
function MyCtrl($scope) {
     $scope.items = [
  {
    "title": "1",
    "myChoice" :"",
      "choices": {
        "pizza": {
          "type": 1,
          "arg": "abc"
        },
        "burger": {
          "type": 1,
          "arg": "pqr"
        }
      }
   },
   {
    "title": "2",
     "myChoice" :"",
      "choices": {
        "pizza": {
          "type": 1,
          "arg": "abc"
        },
        "burger": {
          "type": 1,
          "arg": "pqr"
        }
      }
   }
  ];
  $scope.items = angular.copy($scope.items).filter(function(item){
    item.choices = Object.keys(item.choices).map(function(choice){
        item.choices[choice].keyName = choice;
        return item.choices[choice];
    });
    return item;
  });
  $scope.selection = function(selected){
  console.log(selected);
  }
}

/* Styles go here */