[R] Apply a function to each cell of a ragged matrix
Liaw, Andy
andy_liaw at merck.com
Wed Feb 18 00:26:07 CET 2004
> sapply(split(x,f), sum)
daytime night
12 9
HTH,
Andy
> From: XIAO LIU
>
> R-Helpers:
>
> There are a matrix x and a factor f. nrow(x) == length(f), e.g.:
> x <- matrix(1:6, nrow = 3)
> f <- factor(c("daytime", "daytime", "night"))
>
> I want the sum of all elements of rows of "x" for each
> corresponding level in factor "f",
> In this case, I want output like:
> "daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2]
> "night" [2] x[3,1]+x[3,2]
>
> But, tapply(x,f,sum) or by(x,f,sum) do not work. What other
> functions can I use?
>
> Thank you very much
>
> Xiao
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