filter of related selects in ng-options
<p>I have two (three) <code>select</code> tags that list the same options (brans). I would like to prevent user of choosing the same values in these selects. </p>

<p>controller:</p>

<pre><code>$scope.brands = [
  {id: '1', name: 'Peugeot'},
  {id: '2', name:'BMW'},
  {id: '3', name:'Mercedes'}
];
</code></pre>

<p>In template I tried to use <code>filter</code> filter in two ways:</p>

<pre><code>&lt;body ng-controller="FilterCtrl"&gt;
&lt;div&gt;
  &lt;select ng-model="conf.brand1" ng-options="b.id as b.name for b in brands"&gt;&lt;/select&gt;
&lt;/div&gt;

&lt;div&gt;
  &lt;select ng-model="conf.brand2"
          ng-options="b.id as b.name for b in brands | filter : !conf.brand1 : true"&gt;&lt;/select&gt;
&lt;/div&gt;

&lt;div&gt;
  &lt;select ng-model="conf.brand2"
          ng-options="b.id as b.name for b in brands | filter : conf.brand1 : compareBrands"&gt;&lt;/select&gt;
&lt;/div&gt;
&lt;/body&gt;
</code></pre>

<p>with <code>compareBrands</code> function:</p>

<pre><code>$scope.compareBrands = function(id, already_selected) {
  return id != already_selected;
}
</code></pre>

<p>none of this is working. Here is a <a href="https://plnkr.co/edit/Ta5OViS6fWxjQEy3Zleq?p=preview" rel="nofollow">plunker</a> of my problem.</p>

<p>Thank you.</p>