Added average filter to math module

README.md

@@ -54,6 +54,7 @@
 - [Math](#math)
   - [min](#min)
   - [max](#max)
+  - [average](#average)
   - [percent](#percent)
   - [radix](#radix)
   - [sum](#sum)
@@ -1017,6 +1018,30 @@ min find and return the lowest number in a given array
 <!--
 result:
 1
+-->
+```
+
+###average
+
+Average number of some property in given array
+
+```js
+$scope.scores = [
+    { name: 'Dan', score: 10 },
+    { name: 'Edd', score: 20 },
+    { name: 'Edi', score: 30 },
+    { name: 'Ari', score: 40 },
+    { name: 'Tod', score: 50 }
+  ];
+```
+```html
+<p> {{ scores | average: 'score' }}</p>
+
+<!--
+result:
+30
+-->
+
 ```
 ###percent
 Percentage between two numbers<br/>

src/_filter/math/average.js

@@ -0,0 +1,24 @@
+/**
+ * @ngdoc filter
+ * @name average
+ * @kind function
+ *
+ * @description
+ * calculate average number of some property in given array
+ */
+
+angular.module('a8m.math.average', ['a8m.math'])
+
+  .filter('average', function() {
+  return function(collection, prop) {
+
+    if(!angular.isArray(collection)) {
+      return collection;
+    }
+    var sum = 0;
+    angular.forEach(collection,function(ele) {
+      sum += ele[prop];
+    });
+    return sum/collection.length;
+  };
+});

test/spec/filter/math/average.js

@@ -0,0 +1,34 @@
+'use strict';
+
+describe('averageFilter', function () {
+
+  var filter;
+  var array = [
+      { name: 'Dan', score: 80 },
+      { name: 'Edd', score: 90 },
+      { name: 'Edi', score: 40 },
+      { name: 'Ari', score: 87 },
+      { name: 'Tod', score: 99 }
+    ];
+
+  beforeEach(module('a8m.math.average'));
+
+  beforeEach(inject(function ($filter) {
+    filter = $filter('average');
+  }));
+
+
+  it('should get an array of numbers and return its average', function() {
+
+    expect(filter(array, 'score')).toEqual(79.2);
+  });
+
+  it('should get an !array and return it as-is', function() {
+
+    expect(filter('angular', 'name')).toEqual('angular');
+    expect(filter({})).toEqual({});
+    expect(filter(!0)).toBeTruthy();
+
+  });
+
+});