[R] grouped colSums without for loops?

From: Hans Ekbrand <hans_at_sociologi.cjb.net>
Date: Tue, 18 Mar 2008 11:41:46 +0100

Consider the following data.frame, d.

d <- data.frame(c("a","b","c","d","b","a"), c(1,4,85,3,4,1), c(7,6,2,4,15,33)) names(d) <- c("foo", "bar", "baz")  

To get the colsum of d[[2]] for the rows that have d$foo == "a" I know I can use

colSums(subset(d, d[[1]] == "a", select = 2))

But what is needed to get a list of colSums for d[[2]] for each factor of d$foo ? Can it be done without a for loop?

Hans Ekbrand (http://sociologi.cjb.net) <hans@sociologi.cjb.net>
GPG Fingerprint: 1408 C8D5 1E7D 4C9C C27E 014F 7C2C 872A 7050 614E

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Received on Tue 18 Mar 2008 - 10:45:16 GMT

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