Remove rowgrouping

am using DataTables Row Grouping Add-on. I used it by select box change event.

Code

In PHP :

<select id="Group-Discoveries" name="Group-Discoveries" class="input-medium">
<option value="">None</option>
<option value="6">Domain</option>
<option value="7">Type</option>
<option value="8">Category</option>
<option value="9">Status</option>
</select>

In JS :

$(document).ready(function() {    
var DTable = $('#discovery').dataTable( {
            "sDom": "<'row-fluid'<'span3'<'toolbar'>><'span3'<'selectbar'>><'span6'f>r>t<'row-fluid'<'span6'i><'span6'p>>",
            "bPaginate": false
        });
        $('#Group-Discoveries').live('change', function(){
            var index = $(this).val();
            if(index == ''){

            }
            else{
                DTable.rowGrouping({
                    "iGroupingColumnIndex": index,
                    "bHideGroupingColumn": false,
                    "bHideGroupingOrderByColumn": false,
                    "sGroupingClass":"group_"+index,
                    "bSetGroupingClassOnTR":true,
                    "bExpandableGrouping":true
                });
            }
        });
});

I want to remove rowgrouping when the index is empty.

Thanks.