Great question. I'll use it for an article in the February Crystal Clear.
A TopN of the -Summary gives you the same result as the Bottom N.
Conditional TopN/Bottom N
1) Create a parameter {?Top/Bottom}
2) Create a formula {@Sort}
If {?Top/Bottom} ="Top" then {table.value}
else -{table.value}
3) Create a subtotal of this in your group and suppress it.
4) use TopN to do a Sort on this subtotal (Ascending)
Conditional number of groups
1)create a parameter {?Group}
2) Do conditional section suppress GH, D and GF of
GroupNumber > {?Group}
Email me (bruce@chelseatech.co.nz) and I'll send the report I used to test this out. Editor and Publisher of Crystal Clear