Code:
Ext.define('myGrid', {
    extend: 'Ext.grid.Panel',
    features: [Ext.create('Ext.grid.feature.Grouping', {
        groupHeaderTpl: '{name} ({rows.length})',
        hideGroupedHeader: true,
        startCollapsed: true,
        id: 'assetTypeGrouping'
    })],....
Please guide me....