Suppose I have:

Book	Value	
A	10	
B	11	
C	9	
D	8	
A	12	
C	4	
D	5	
B	7	

I want to summarize above not by Book but by groupings of Books as in
(below)

I have a list ... basic_map <- list(c("A",B"),c("C,D"))
Big_names <- c("A1", "A2")
Names(basic_map) <- big_names

So I want to get :

A1 40
A2 26

How do I use tapply AND the list to get my custom groupings?

thx
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