function _fnDetectHeader ( aLayout, nThead )
	{
		var nTrs = $(nThead).children('tr');
		var nTr, nCell;
		var i, k, l, iLen, jLen, iColShifted, iColumn, iColspan, iRowspan;
		var bUnique;
		var fnShiftCol = function ( a, i, j ) {
			var k = a[i];
	                while ( k[j] ) {
				j++;
			}
			return j;
		};
	
		aLayout.splice( 0, aLayout.length );
	
		/* We know how many rows there are in the layout - so prep it */
		for ( i=0, iLen=nTrs.length ; i<iLen ; i++ )
		{
			aLayout.push( [] );
		}
	
		/* Calculate a layout array */
		for ( i=0, iLen=nTrs.length ; i<iLen ; i++ )
		{
			nTr = nTrs[i];
			iColumn = 0;
	
			/* For every cell in the row... */
			nCell = nTr.firstChild;
			while ( nCell ) {
				if ( nCell.nodeName.toUpperCase() == "TD" ||
				     nCell.nodeName.toUpperCase() == "TH" )
				{
					/* Get the col and rowspan attributes from the DOM and sanitise them */
					iColspan = nCell.getAttribute('colspan') * 1;
					iRowspan = nCell.getAttribute('rowspan') * 1;
					iColspan = (!iColspan || iColspan===0 || iColspan===1) ? 1 : iColspan;
					iRowspan = (!iRowspan || iRowspan===0 || iRowspan===1) ? 1 : iRowspan;
	
					/* There might be colspan cells already in this row, so shift our target
					 * accordingly
					 */
					iColShifted = fnShiftCol( aLayout, i, iColumn );
	
					/* Cache calculation for unique columns */
					bUnique = iColspan === 1 ? true : false;
	
					/* If there is col / rowspan, copy the information into the layout grid */
					for ( l=0 ; l<iColspan ; l++ )
					{
						for ( k=0 ; k<iRowspan ; k++ )
						{
							aLayout[i+k][iColShifted+l] = {
								"cell": nCell,
								"unique": bUnique
							};
							aLayout[i+k].nTr = nTr;
						}
					}
				}
				nCell = nCell.nextSibling;
			}
		}
	}
Use the DOM source to create up an array of header cells. The idea here is to
create a layout grid (array) of rows x columns, which contains a reference
to the cell that that point in the grid (regardless of col/rowspan), such that
any column / row could be removed and the new grid constructed
 @param array {object} aLayout Array to store the calculated layout in
 @param {node} nThead The header/footer element for the table
 @memberof DataTable#oApi