title: puuting validation on submit button for lodash filter
body: <p>I have three dropdowns:</p>
  
  <pre><code> &lt;form name="myForm" ng-submit="save(myForm.$valid)" novalidate="novalidate"&gt;
  
  &lt;div class="form-group"&gt;
   &lt;label&gt;Values:&lt;/label&gt;   
   &lt;label&gt;First&lt;/label&gt;
  &lt;select ng-model="a.values[0]" ng-change="check()"&gt;
   &lt;option value="1"&gt;1&lt;/option&gt;
   &lt;option value="2"&gt;2&lt;/option&gt;
   &lt;option value="3"&gt;3&lt;/option&gt;
   &lt;option value="4"&gt;4&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;label&gt;Second&lt;/label&gt;
  &lt;select ng-model="a.values[1]" ng-change="check()"&gt;
   &lt;option value="1"&gt;1&lt;/option&gt;
   &lt;option value="2"&gt;2&lt;/option&gt;
   &lt;option value="3"&gt;3&lt;/option&gt;
   &lt;option value="4"&gt;4&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;label&gt;Third&lt;/label&gt;
  &lt;select ng-model="a.values[2]" ng-change="check()"&gt;
   &lt;option value="1"&gt;1&lt;/option&gt;
   &lt;option value="2"&gt;2&lt;/option&gt;
   &lt;option value="3'&gt;3&lt;/option&gt;
   &lt;option value="4"&gt;4&lt;/option&gt;
  &lt;/select&gt;
  &lt;/div&gt;
  
  &lt;button type="submit" class="btn btn-success"&gt;Save &lt;/button&gt;
  </code></pre>
  
  <p></p>
  
  <p>On these dropdowns I applied a filter:-</p>
  
  <pre><code>scope.check = function() {
    if (_.uniq(scope.a.values).length !== scope.a.values.length) {
      scope.notify("error", "Please set unique values");
    }
  };
  </code></pre>
  
  <p>What I want is if the values on dropdowns are not unique then on save button it shows error. Please note that these are not required fields so validation related to that is not required. Only if user set same values then only on save it shows error.</p>