A simple AngularJS filter for summarizing the values of an array containing objects by a key.

example.html

<!-- $scope.myList = [{name: 'Foo', total: 1}, {name: 'Bar', total: 2}, {name: 'Baz', total: 3}] -->
<span class="badge badge-success pull-right">{{myList|sumByKey:'total'}}</span>

SumByKey.js

angular.module('caco.feed.filter', [])
    .filter('sumByKey', function() {
        return function(data, key) {
            if (typeof(data) === 'undefined' || typeof(key) === 'undefined') {
                return 0;
            }

            var sum = 0;
            for (var i = data.length - 1; i >= 0; i--) {
                sum += parseInt(data[i][key]);
            }

            return sum;
        };
    });