groups - Crystal Reports Dynamic Groupings -

i new in crystal reports don't know do

how can make group formula:
in main report

if distinctcount ({prod.group_id}, {prod.id_no})=1 //group prod.group_id else if distinctcount ({prod.group_id}, {prod.id_no})>1 ,     ({prod.group_id}=previous({prod.group_id}) or     {prod.group_id}=next({prod.group_id})) //group      prod.doc_id else //group      prod.group_id 

please me new in crystal reports , need make badly

i have in main report:

in group header , group {prod.group_id}
sub_car
sub_airplane

some of sub reports working when group {prod.group_id} , sub reports works when group {prod.doc_id}

you trying group result of grouping regroup not possbile way wrote formula because distinctcount ({prod.group_id}, {prod.id_no}) output of grouping.

to achive need use sub report , pass distinct count use grouping in sub report.

take section group footer b , place sub report there , using change sub report links pass distinctcount ({prod.group_id}, {prod.id_no}) sub report

in sub report appearing in parameter fields {?distinctcount ({prod.group_id}, {prod.id_no})} create formula @grouping , write below code:

if {?distinctcount ({prod.group_id}, {prod.id_no})}=1 //group prod.group_id else if {?distinctcount ({prod.group_id}, {prod.id_no})}>1 ,     ({prod.group_id}=previous({prod.group_id}) or     {prod.group_id}=next({prod.group_id})) //group prod.doc_id else //group prod.group_id 

now use formula group sub report... if wish display data in main report or remove fields of main report , show sub report