example.html

<html>
<head>
	<link rel="stylesheet" href="http://cdn.datatables.net/1.10.7/css/jquery.dataTables.min.css">

	<script src="http://code.jquery.com/jquery-2.1.4.min.js"></script>
	<script src="http://cdn.datatables.net/1.10.7/js/jquery.dataTables.js"></script>
	<script src="dataTables.rowsGroup.js"></script>
</head>
<body>
	<button id="update_btn">Manual remerge cells</button>
	<table id="example" class="display"></table>
<script>
$(function(){
	var data = [
		['subgroupN', 'Group1', 'sub-subgroupN', 'ElementN', '2Element N'],
		['subgroup1', 'Group2', 'sub-subgroup1', 'Element1', '2Element 1'],
		['subgroup2', 'Group2', 'sub-subgroup1', 'Element1', '2Element 1'],
		['subgroup2', 'Group2', 'sub-subgroup1', 'Element2', '2Element 2'],
		['subgroup2', 'Group2', 'sub-subgroup2', 'Element3', '2Element 2'],
		['subgroup2', 'Group2', 'sub-subgroup2', 'Element4', '2Element 4'],
		['subgroup2', 'Group2', 'sub-subgroup2', 'Element2', '2Element 2'],
		['subgroup3', 'Group1', 'sub-subgroup1', 'Element1', '2Element 1'],
		['subgroup3', 'Group1', 'sub-subgroup1', 'Element1', '2Element 1'],
		['subgroup2', 'Group2', 'sub-subgroup2', 'Element1', '2Element 1'],
		['subgroup4', 'Group2', 'sub-subgroup2', 'Element1', '2Element 1'],
		['subgroup4', 'Group2', 'sub-subgroup3', 'Element10', '2Element 17'],
		['subgroup4', 'Group2', 'sub-subgroup3', 'Element231', '2Element 211'],
		
	]
	var table = $('#example').DataTable({
		columns: [
			{
				title: 'First group',
			},
			{
				name: 'second',
				title: 'Second group [order first]',
			},
			{
				title: 'Third group',
			},
			{
				title: 'Forth ungrouped',
			},
			{
				title: 'Fifth ungrouped',
			},
		],
		data: data,
		lengthChange: false,
		searching: true,
		paging: false,
		order: [],
		rowsGroup: [// Always the array (!) of the column-selectors in specified order to which rows groupping is applied
					// (column-selector could be any of specified in https://datatables.net/reference/type/column-selector)
			'second:name',
			0,
			2
		],
	})
	table.draw(false);
	$('#update_btn').click(function(){
		table.rowsgroup.update();
	})
});

</script>
</body>
</html>