code: function select (index) {
      // force form to update state for validation
      $mdUtil.nextTick(function () {
        getDisplayValue(ctrl.matches[ index ]).then(function (val) {
          var ngModel = elements.$.input.controller('ngModel');
          $mdLiveAnnouncer.announce(val + ' ' + ctrl.selectedMessage, 'assertive');
          ngModel.$setViewValue(val);
          ngModel.$render();
        }).finally(function () {
          $scope.selectedItem = ctrl.matches[ index ];
          setLoading(false);
        });
      }, false);
    }
docs: Selects the item at the given index.
  @param {number} index to select