Aggregating by a grouping

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

Try this:

testdf <- data.frame(book=factor(c("A", "B", "C", "D", "A", "C", "D", 
"B")),  value=c(10,11,9,8,12,4,5,7))
bookgroup <- rep("A1", nrow(testdf))
bookgroup[testdf$book=="C" | testdf$book=="D"] <- "A2"
tapply(testdf$value, bookgroup, sum)

Regards,
Richie.

Mathematical Sciences Unit
HSL


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