jQuery Grid Plugin - jqGrid

In my grid below i have 2 levels of grouping

and my grid is

colModel:[
                {name:'szGroupAccType',index:'szGroupAccType'},
                {name:'szAccTypeId',index:'szAccTypeId'},
                {name:'szAccNm',index:'szAccNm', width:500,
                    formatter: function (cellValue, options, rowObject, actions) {
                        if (options.rowId === "") {
                            var names = [], data, i, l, item;
                            if (options.rowId === "" && typeof actions === "undefined") {

                                data = $(this).jqGrid("getGridParam", "data");
                                //here to set accounts on total
                            }
                            return cellValue;
                        } else {
                            return '<span style="display:inline-block;left:25px;position:relative;">' +
                                cellValue;
                        }
                    },
                    summaryType:'count', summaryTpl : 'Total ({0}) '},
                {name:'Balance',index:'Balance',align:'right',formatter: numberFormatter, sorttype:"float", summaryType:'sum', formatoptions:{thousandsSeparator:","}},
                {name:'szAccCode',index:'szAccCode', hidden:true}
            ],
            grouping:true, 
            groupingView : { 
                groupField : ['szGroupAccType', 'szAccTypeId'], 
                groupSummary : [true, true], 
                groupColumnShow : [false, false], 
                groupText : ['<b>{0}</b>', '{0}'], 
                groupCollapse : false, 
                groupOrder: ['asc', 'asc'],
                showSummaryOnHide: true
            },

i hv problem with this line
data = $(this).jqGrid("getGridParam", "data");

i've checked with firebug and var data is empty. Could you tell me where i did wrong? I'm trying to change total (in yellow) to Aktiva Tetap (110-...Bank dollar, 120- ... Bank rupiah) and total in grey with Asset (Aktiva Tetap (110-...Bank dollar, 120- ... Bank rupiah)) and so on.
Thanks in advance