I have a matrix with a set of variables one of which is a factor. Using by()
I have calculated something about each group (say the sum). Now I want to
create a new variable in the original matrix that contains the results of
the by() for each observation that is in the corresponding group.

For example I have:

---------

a <-c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16)

b <-c(7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22)

e <-c("A","B","C","D","E","F","A","B","C","D","E","F","D","E","F","A")

f <-data.frame(e,a,b)

# Calculate sum by group

sums <- by(f, e, function(x) sum(x$b))

-----------

Now I would like to assign each observation in f a new variable based on the
results of the by(). I converted sums into a matrix and then tried using
match() and ifthen() but could not get it to work.

Thanks,

EG

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