What is the best way to group a bunch of data and minus another group of data in a table format and append it back?

I have a following situation: some commands | table Type, Value which results in: Type, Value ========= A, 5 B, 5 C, 1 D, 0 I need to add up A,B and subtract C,D and append them back to the table like this as another value Type="E": Type, Value ========= A, 5 B, 5 E, 9 <- 5+5-(1+0) Any ideas?