Crystal Reports field sum

Message

   Hi

I've a codart field in the detail section and for each codart filed I've a total

Now I need for every codart found the sum of the total

so If I've in my details section

product    total

aaa          1
bbb          2
ccc           3
aaa         5
bbb         6

In the report footer I would like to have

aaa= 6
bbb=8
ccc=3

I think that the only way to obtain this is using two arrays but I don't know how to corretcly do that

Anyone have an example?

thanks