aoColumns in table header

To begin with I want to thank you for a great plugin.
I use it for few years and everything suit.
Now I need to aoColumns defined in table header.
I do so:

oTable=$('#table').dataTable( {
	"sAjaxSource": "table.json",
        "sPaginationType": "full_numbers" ,
	"aaSorting": [[2,'desc']],
} );
var columns=oTable.fnSettings().aoColumns;
$('#table thead th').each(function(i){
	if(typeof $(this).attr('bSortable')!='undefined')columns[i].bSortable=$(this).attr('bSortable');
	if(typeof $(this).attr('sType')!='undefined')columns[i].sType=$(this).attr('sType');
	if(typeof $(this).attr('sClass')!='undefined')columns[i].sClass=$(this).attr('sClass');
});

The problem is that the sType is not defined in this way.
Column sorting as default type.
But if you define sType in the table initialization, then everything works correctly.
What do i do wrong?
thanks.