datagrid判断数据是否可以合并并合并单元格

function _setDefaultMearge() {
var rows = $("#tt").datagrid('getRows');
var len = rows.length;
var preIndex = 0;
for (var i = preIndex; i< len; i++) {
var cityCode = rows[i].CITY_CODE;
var cityCodeNum = 1;
for (var j = i+1; j< len; j++) {
if (cityCode == rows[j].CITY_CODE) {
cityCodeNum++;
} else {
break;
}
}
$('#tt').datagrid('mergeCells', {
index: i,
field: "CITY_NAME",
rowspan: cityCodeNum
});
preIndex = cityCodeNum+i;

}
}