forumla that filters data together

Hi,

i currently got an invoice system that has all sales made from various customers and then i have customers that has brought many items on different dates. is there a formula that when i could press on a command button and it can combine only certain customers together for example

customer name
harry
tom
harry
harry
john
smith

i want to able to combine all the harry's together in a summary sheet

hope i made things clear

thanks