function order_by(){
    var params = window.location.search.substr(1);
	if (params.length > 0){
		var arr=window.location.search.substr(1).split("&");
		var length = arr.length+2;
	}else{
		var length = 2;
		var arr=new Array(0);
	}
	var keys = new Array(length);
	var values = new Array(length);
	var existOrder = false;
	var existOrderBy = false;
   for(var j=0;j<arr.length;j++){
		 a=arr[j].split("=");   
		keys[j] = a[0];
		values[j] = a[1];
		 if ( a[0] == "orderby"){
				length--;
				existOrderBy = true;
				values[j]=arguments[0];
		}
		 if ( a[0] == "order"){
				length--;
				existOrder = true;
			if (a[1] == "asc"){ values[j] = "desc"; }
			else {
				values[j] ="asc";
			}
		}
   }
   if ( length == (arr.length+1) && existOrderBy){
		keys[length -1] = "order";
		values[length -1] = "asc";
   }else if ( length == (arr.length+1) && existOrder){
		keys[length -1] = "orderby";
		values[length -1] = arguments[0];
	}else if ( length == (arr.length+2)){
	    keys[length -1] = "orderby";
	    values[length -1] = arguments[0];
		keys[length -2] = "order";
		values[length -2] = "asc";
	}
		var res = new Array(length);
		for(var k =0;k<length;k++){ res[k] = (keys[k] + "=" + values[k]); }
		url = window.location.pathname +"?"+ res.join("&") ;
		window.location=url;
}