Angular JS动态下拉选择基于其他下拉选择

Question

问题：
 我能够使用ng repeat和ng-options创建一组下拉列表，并从下一个下拉列表中删除所选项目。

这里的问题是它不是动态的，适用于预定义的下拉数量。

当前逻辑适用于三个下拉菜单，如果我想扩展到另一个下拉菜单，代码中还有一个额外的过滤器和下拉列表更改

HTML：

<div ng-app="myApp">
  <div ng-controller="HelloCntl">
  <ul>
    <li ng-repeat="friend in friends | filter:{name:'!Adam'}">
        <span>{{friend.name}}</span>
        <span>{{friend.phone}}</span>
    </li>
  </ul>
  <select ng-model="selectname1" 
    ng-options="item as item.name for item in friends|filter:filter2|filter:filter3" ><option value="">- select -</option></select>
   <div>{{selectname1}}</div>

  <select ng-model="selectname2" 
      ng-options="item as item.name for item in friends|filter:filter1|filter:filter3" ><option value="">- select -</option></select>
   <div>{{selectname2}}</div>

  <select ng-model="selectname3" ng-options="item as item.name for item in friends|filter:filter1|filter:filter2" ><option value="">- select -</option></select>
   <div>{{selectname3}}</div>
 </div>
</div>

JS：

var app = angular.module('myApp',[])

app.controller('HelloCntl',  
    function ($scope) {
    $scope.selectname1={};    
    $scope.selectname2={};    
    $scope.selectname3={};

    $scope.filter1 = function(item){
      return (!($scope.selectname1&&$scope.selectname1.id)||item.id !=$scope.selectname1.id);
    };

    $scope.filter2 = function(item){
      return (!($scope.selectname2&&$scope.selectname2.id)||item.id!=$scope.selectname2.id);
    };
    $scope.filter3 = function(item){
      return (!($scope.selectname3&&$scope.selectname3.id)||item.id !=$scope.selectname3.id);
    };
    $scope.friends = [
      {
        id:1,name: 'John',
        phone: '555-1276'},
      {
        id:2,name: 'Mary',
        phone: '800-BIG-MARY'},
      {
        id:3,name: 'Mike',
        phone: '555-4321'},
      {
        id:4,name: 'Adam',
        phone: '555-5678'},
      {
        id:5,name: 'Julie',
        phone: '555-8765'}

    ];


})

http://codepen.io/nagasai/pen/bBjmqx