Make formulae for each group/parameter as follows
(assumes your parameters are boolean (ie group by customer true/false);
GROUP 1
if {?group_id} = True then {table.group_id} else ""
GROUP 2
if {?customer} = True then {table.customer} else ""
GROUP 3
if {?category} = True then {table.category} else ""
GROUP 4
if {?product} = True then {table.product} else ""
Then create your groups on the relevant formulas rather than the actual table fields - eg your first group would be on formula
{@Group 1} rather than {table.group_id}
If you need any more help let me know.
Regards,
Ryan.
Edited by rkrowland - 01 Feb 2012 at 1:15am