Randomising array in angularjs using filter method

I have some filter options for my array like this:

$scope.sortableItems = {    'random' : 'Filter Random',
                                'test1' : 'Filter test1',
                                'test2' : 'Filter test2',
                                'test3' : 'Filter test3'
                            };

Then I set:

$scope.sortKey =  'random';
$scope.reverse = false;

And my array is created like this:

for (var i = 0; i < $scope.jsonData.length; i++) {
        var item = { "test1": $scope.jsonData[i].test1, "test2": $scope.jsonData[i].test2, "test3" : $scope.jsonData[i].test3};
        $scope.results.push(item);
}

Then I use:

$scope.results = $filter('orderBy')($scope.results, $scope.sortKey, $scope.reverse);

in order to filter it the list. However, how would I accomplish to "randomly filter" the list in this scenario?