JQgrid Custom Filter


Can you please help on this functionality. I am searching in google for this functionality but till now am not getting any link for this.

My requirement is. I created one filter toolbar in the header in jqgrid. i created one column is called ‘End Date’ which is a drop down menu. I loaded two values ‘next 90 days’ and ‘next 180 days’. when i select next 90 days it will be filtered the data based on dropdown value. i have given my code. Please check and let me know if i wrong any thing below the code.

var mygrid = jQuery("#gridcontactalerts").jqGrid({
		url: "assets/json/contactalertdata.json",
		datatype: "json",
		colNames:['Date','Type','Category','Note','End Date'],
			{name:'enddate',index:'enddate',stype:'select', formatoptions:{baseLinkUrl:'index.html', addParam: ''}, align:"left", sorttype:"date",editoptions:{value:":All;Next 90 Days:Next 90 Days;Next 180 Days:Next 180 Days"},searchoptions:{dataEvents:[{type:'change',fn:function(e){dateResult(e.target.value)}}]}}
jsonReader : { repeatitems: true, cell: "", id: "1"}


function dateResult(v){
	var g = $('#gridcontactalerts');

		var curdateobj = new Date();
		var curmonth = curdateobj.getMonth()+1;
		var curdate = curdateobj.getDate();
		var curyear = curdateobj.getFullYear();
		var today = (curmonth)+'/'+curdate+'/'+curyear;
		var d;
		if(v=="Next 90 Days")
			d = (curmonth+3)+'/'+curdate+'/'+curyear;
		else if(v=="Next 180 Days"){
			d = (curmonth+6)+'/'+curdate+'/'+curyear;
		var f = {groupOp:"AND",rules:[]};
		g[0].p.search = true;

Its not filtertering the data when i select the values from the dropdown. Can you please check and let me know.