have a report that is grouoped by a date field

In the group options there I see I can change to
display data by:

for each day
for each week

Can I change that option dynamically say using a parameter value or a formula?

say: Ask the user to group dates by day by week?

I know I can do two reports but that means mainting two reports instead of one

Any help is appreciated

Okay  I will give this  a try