[R] Apply functions along "layers" of a data matrix

[Paul Hiemstra]

On 11/18/2011 01:05 PM, saschaview at gmail.com wrote:
> daf <- data.frame(
>   'id' = rep(1:5, 3),
>   matrix(1:60, nrow=15, dimnames=list( NULL, paste('v', 1:4, sep='') )),
>   rep = rep(1:3, each=5)
> )
Hi,

This seems like a job for plyr!

library(plyr)
ddply(daf, .(rep), summarise, mn = mean(v1))

hope this helps,
Paul

-- 
Paul Hiemstra, Ph.D.
Global Climate Division
Royal Netherlands Meteorological Institute (KNMI)
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