[R] paired t-test. Need to rearrange data?

[Petr Pikal]

Hi

one possibility is

t(unstack(test.data, y~id))

HTH
Petr

On 6 Aug 2006 at 16:13, Henrik Parn wrote:

Date sent:      	Sun, 06 Aug 2006 16:13:29 +0200
From:           	Henrik Parn <henrik.parn at bio.ntnu.no>
Organization:   	NTNU
To:             	R-help <r-help at stat.math.ethz.ch>
Subject:        	[R] paired t-test. Need to rearrange data?
Send reply to:  	henrik.parn at bio.ntnu.no
	<mailto:r-help-request at stat.math.ethz.ch?subject=unsubscribe>
	<mailto:r-help-request at stat.math.ethz.ch?subject=subscribe>

> Dear all,
> 
> I have received some data arranged like this:
> 
> # original data
> id <- rep(letters[1:6], each=2)
> time <- as.factor(rep(1:2, 6))
> y <- as.vector(replicate(6, c(rnorm(n=1, mean=1), rnorm(n=1,
> mean=2)))) test.data <- data.frame(id, time, y) test.data
> 
> I would like to perform a paired t-test of the y-values at time=1
> against those at time=2, with samples paired by their id. Is it
> necessary to arrange the data in a format like this:   
> 
> # rearranged data
> id <- letters[1:6]
> y1 <- replicate(6, rnorm(n=1, mean=1)) # y-value at time = 1
> y2 <- replicate(6, rnorm(n=1, mean=2)) #  y-value at time = 2
> test.data2 <- data.frame(id, y1, y2)
> test.data2
> 
> ...in order to perform a paired t-test?
> t.test(y1, y2, paired=T)
> 
> If yes, which is the most convenient way to rearrange the data?
> Or is it possible to apply the paired t-test function to the original
> data set?
> 
> And a side question: In my examples, I suppose can I use set.seed to
> reproduce the 'rnorm-values' created in the 'original data' also in my
> the 'rearranged data'. Can someone give me a hint of how to apply the
> same 'seed' to all the rnorms?
> 
> 
> Thanks a lot in advance!
> 
> 
> Henrik
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html and provide commented,
> minimal, self-contained, reproducible code.

Petr Pikal
petr.pikal at precheza.cz