unique filter not working properly in Angular.js
<p>I have a simple example where I am exptecting my paragraphs to filter out values based on unique age, but I get the unknown provider error. How ? </p>

<pre><code>&lt;html&gt;
&lt;head&gt;
&lt;script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.4.8/angular.min.js"&gt;&lt;/script&gt;
&lt;/head&gt;
&lt;body ng-app="myApp" ng-controller="myCtrl"&gt;
    &lt;p ng-repeat="x in persons | unique: 'age'"&gt;{{x.name}}&lt;/p&gt;
&lt;script&gt;
//App declaration
var app = angular.module('myApp',[]);
//Controller Declaration
app.controller('myCtrl',function($scope){
    $scope.persons = [{name: "Peter",age:23},{name:"Laila",age:25},{name:"Rosy",age:23}];
});
&lt;/script&gt;
&lt;/body&gt; 
&lt;/html&gt; 
</code></pre>

<p><a href="https://i.stack.imgur.com/ZBgZJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZBgZJ.png" alt="enter image description here"></a></p>