results[i].sort is not a function

for (var i = 0, len = myArr.Items.length; i < len; i++) {
                        var id_art = myArr.Items[i].id_a;
                        if (id_art == id_url) {
                            results[i] = myArr.Items[i];
                             results[i].sort(function (a, b) {
                                if (a.results[i].id != b.results[i].id) {
                                    return (a.results[i].id - b.results[i].id);
                                }
                            }); 
                        }
                    }
                    console.log(results);