From: Petr Pikal <petr.pikal_at_precheza.cz>

Date: Wed 09 Aug 2006 - 00:32:28 EST

R-help@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. Received on Wed Aug 09 00:42:59 2006

Date: Wed 09 Aug 2006 - 00:32:28 EST

- Forwarded message follows ------- From: Petr Pikal <petr.pikal@precheza.cz> To: Henrik Parn <henrik.parn@bio.ntnu.no> Subject: Re: [R] paired t-test. Need to rearrange data? Date sent: Tue, 08 Aug 2006 16:13:47 +0200

Hi

Uff, it takes me a bit headache but this shall do it

?unstack ?table ?t

new.list<-unstack(test.data,y~id)

new.test.data<-t(as.data.frame(new.list[table(test.data$id)>1]))
# if you have more than 2 catches you need to modify this^^^
t.test(new.test.data[,1], new.test.data[,2], paired=T)

**HTH
**

Petr

On 7 Aug 2006 at 16:43, Henrik Parn wrote:

Date sent: Mon, 07 Aug 2006 16:43:45 +0200 From: Henrik Parn <henrik.parn@bio.ntnu.no> Send reply to: henrik.parn@bio.ntnu.no Organization: NTNU To: Petr Pikal <petr.pikal@precheza.cz> Subject: Re: [R] paired t-test. Need to rearrange data?

*> Dear Peter,
**>
**> Thanks a lot for your rapid answer! I am afraid that I presented an
**> example data set in my previous question that was to nicely
**> organised. In fact it more looked like the data I want to acheive
**> rather than the data I recieved...
**>
**> So,may I bother you with a follow-up question:
**>
**> I have data on morphology on birds from several different years.
**> Each year about 50-100 birds are captured, marked with a unique id
**> and measured. The recapture rate is very low and on average 1-2
**> birds are recaptured the subsequent year. Again a small example data
**> set, which hopefully is more realistic:
**>
**> ####
**> year <- as.factor(rep(1:4,each= 5)) # the four study years
**> id <- c("a", "b", "c", "d", "e", "b", "f", "g", "h", "a", "i",
**> "g", "j", "k", "l", "j", "m", "n", "l", "o") # id of the birds
**> captured y <- rnorm(20) # the measure taken test.data <-
**> data.frame(year, id, y)
**> ####
**>
**>
**> So, in this small example, bird "a" and "b" is captured on year 1
**> and recaptured year 2, bird "g" captured on year 2 and 3, and so on.
**> On birds that are captured more than once, I would like to do a
**> paired t.test where I compare the measure taken at first capture
**> with that taken on the second time.
**>
**> I suppose I need to add a vector indicating whether it is the first
**> or second time a bird is captured:
**>
**> ####
**> test.data$time <- ifelse(duplicated(test.data$id), 2, 1)
**> ####
**>
**> But then I am stuck...Do you have a hint of how to proceed? How to
**> select the y-values for which I have both a capture and a recapture?
**>
**> Thanks in advance for taking your time!
**>
**> Best regards,
**> Henrik
**>
**> Petr Pikal wrote:
**>
**> >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@bio.ntnu.no>
**> >Organization: NTNU
**> >To: R-help <r-help@stat.math.ethz.ch>
**> >Subject: [R] paired t-test. Need to rearrange data?
**> >Send reply to: henrik.parn@bio.ntnu.no
**> > <mailto:r-help-request@stat.math.ethz.ch?subject=unsubscribe>
**> > <mailto:r-help-request@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@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@precheza.cz
**> >
**> >
**> >
**>
**> --
**> ************************
**> Henrik Pärn
**> Department of Biology
**> NTNU
**> 7491 Trondheim
**> Norway
**>
**> +47 735 96282 (office)
**> +47 909 89 255 (mobile)
**> +47 735 96100 (fax)
**> ************************
**>
*

- End of forwarded message -------Petr Pikal
petr.pikal@precheza.cz

R-help@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. Received on Wed Aug 09 00:42:59 2006

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