On Wed, Jun 18, 2008 at 9:17 AM, Daren Tan <[EMAIL PROTECTED]> wrote:
>
> Below example has 4 sets of triplicates, without using for loop and
> iteratively cbind the columns, what is the "R-approach" of generating a
> matrix of 8 columns that are the averages and standard deviations ? The
> average and standard deviation columns should be side by side i.e. A.mean
> A.sd B.mean B.sd C.mean C.sd D.mean D.sd
>
t <- matrix(rnorm(120), ncol=12)
colnames(t) <- paste(rep(LETTERS[1:4], each=3), 1:3, sep=".")
# First get your data into a more useful format,
# where explanatory variables are explicitly encoded by
# columns in a data frame.
library(reshape)
tm <- melt(t)
tm <- cbind(colsplit(tm$X2, "\\.", c("trt", "block")), tm)
tm$X2 <- NULL
tm <- rename(tm, c("X1" = "rep"))
head(tm)
# tm is now much easier to work with most R functions
# for your case, you can also use cast in the reshape package:
cast(tm, block ~ trt, c(mean, sd))
cast(tm, . ~ trt, c(mean, sd))
# for more info about the reshape package, see http://had.co.nz/reshape
Hadley
--
http://had.co.nz/
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