Angular groupBy filter

gistfile1.txt

/*
 * Inspired by http://stackoverflow.com/a/20645945
 */

app.filter('groupBy', ['$parse', function ($parse) {
    return function (list, group_by) {

        function addChangedTag (item, field) {
            item[field + '_CHANGED'] = true;
        }

        var filtered = [];
        var prev_item = null;

        // loop through each item in the list
        angular.forEach(list, function (item) {

            // if not the first item
            if (prev_item !== null) {

                // check if any of the group by field changed

                //force group_by into Array
                group_by = angular.isArray(group_by) ? group_by : [group_by];

                //check each group by parameter
                for (var i = 0, len = group_by.length; i < len; i++) {
                    if ($parse(group_by[i])(prev_item) !== $parse(group_by[i])(item)) {
                        addChangedTag(item, group_by[i]);
                    }
                }

            }// otherwise we have the first item in the list which is new
            else {
                for (var i = 0, len = group_by.length; i < len; i++) {
                    addChangedTag(item, group_by[i]);
                }
            }

            filtered.push(item);
            prev_item = item;

        });

        return filtered;
    };
}])