[R] grouped colSums without for loops?

[jim holtman]

Is this what you want?

> lapply(split(d, d$foo), function(x) colSums(x[,-1]))
$a
bar baz
  2  40

$b
bar baz
  8  21

$c
bar baz
 85   2

$d
bar baz
  3   4

>


On Tue, Mar 18, 2008 at 5:41 AM, Hans Ekbrand <hans at sociologi.cjb.net> wrote:
> 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 at sociologi.cjb.net>
> GPG Fingerprint: 1408 C8D5 1E7D 4C9C C27E 014F 7C2C 872A 7050 614E
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?