Dear John, Perhaps is possible to do the job using apply or any of its friends. For now, here is a solution using for() :
# Data sets set.seed(123) sample1<-matrix(data=c(1:20),byrow=TRUE,ncol=5,nrow=4) sample2<-sample1+rnorm(20) # t-test p-values k=nrow(sample1) res=NULL for(i in 1:k) res[i]=t.test(sample1[i,],sample2[i,])$p.value res Another approach could be pag 5 in [1]. HTH, Jorge [1] http://www.amstat-online.org/sections/graphics/newsletter/Volumes/v181.pdf On Thu, Oct 16, 2008 at 12:07 PM, John Sorkin <[EMAIL PROTECTED]>wrote: > Although I am grateful to Jorge and David for their suggestions, their > solution will not solve my problem as sample2 is not fixed. Let me > demonstrate what I want to do: > > > # Define two matricies > sample1<-matrix(data=c(1:20),byrow=TRUE,ncol=5,nrow=4) > sample2<-sample1+rnorm(20) > > These are the computations that I would like to perform using apply (or > some similar method): > > > # Compute t-test comparing first row of sample 1 to first row of sample 2 > t.test(sample1[1,],sample2[1,]) > > # Compute t-test comparing second row of sample 1 to second row of sample 2 > t.test(sample1[2,],sample2[2,]) > > # Compute t-test comparing third row of sample 1 to third row of sample 2 > t.test(sample1[3,],sample2[3,]) > > # Compute t-test comparing fourth row of sample 1 to fourth row of sample 2 > t.test(sample1[4,],sample2[4,]) > > > > As you can see, the code below does not return the same values! It does not > work. > apply(sample1,1,function(x) t.test(x,sample1)$p.value) > > Sugestions would be appreciated! > John > > > > > > > > > John David Sorkin M.D., Ph.D. > Chief, Biostatistics and Informatics > University of Maryland School of Medicine Division of Gerontology > Baltimore VA Medical Center > 10 North Greene Street > GRECC (BT/18/GR) > Baltimore, MD 21201-1524 > (Phone) 410-605-7119 > (Fax) 410-605-7913 (Please call phone number above prior to faxing) > > >>> "Jorge Ivan Velez" <[EMAIL PROTECTED]> 10/16/2008 10:04 AM >>> > Thanks for the correction David! You're absolutely right! A typo :- ) > ... > Cheers, > > Jorge > > > On Thu, Oct 16, 2008 at 10:00 AM, David Winsemius <[EMAIL PROTECTED] > >wrote: > > > > > On Oct 16, 2008, at 8:11 AM, Jorge Ivan Velez wrote: > > > > Dear John, > >> Yes. Assuming that 'sample2' is fixed, something like this should do > what > >> you want: > >> > >> # Data sets > >> set.seed(123) > >> sample1=matrix(rnorm(100),ncol=10) > >> sample2=rnorm(10,5,4) > >> > >> # t-test p-values > >> apply(X,1,function(x) t.test(x,sample2)$p.value) > >> > > > > It seems clear that you meant to type: > > apply(sample1,1,function(x) t.test(x,sample2)$p.value) > > > > > > > >> [1] 0.002348970 0.004733230 0.004810952 0.004907549 0.002342979 > >> 0.018748229 > >> 0.003546655 0.006084410 > >> [9] 0.003100983 0.007007980 > >> > >> > >> HTH, > >> > >> Jorge > >> > >> > >> On Thu, Oct 16, 2008 at 8:01 AM, John Sorkin < > [EMAIL PROTECTED] > >> >wrote: > >> > >> R 2.7.2 > >>> Windows XP > >>> > >>> I am using apply to compute a series of Student's t-test from two > >>> matrices, > >>> sample1 and sample2. > >>> boo<-apply(sample1,1,t.test,sample2) > >>> > >>> I want to pick of the p-values from the tests, but can't seem to get it > >>> to > >>> work. I have tried several methods to get the values including: > >>> boo<-apply(sample1,1,t.test$t.test,sample2) > >>> boo<-apply(sample1,1,t.test,sample2)$t.test > >>> > >>> any suggestions? > >>> > >>> Thanks > >>> John > >>> > >>> John Sorkin M.D., Ph.D. > >>> Chief, Biostatistics and Informatics > >>> Baltimore VA Medical Center GRECC, > >>> University of Maryland School of Medicine Claude D. Pepper OAIC, > >>> University of Maryland Clinical Nutrition Research Unit, and > >>> Baltimore VA Center Stroke of Excellence > >>> > >>> University of Maryland School of Medicine > >>> Division of Gerontology > >>> Baltimore VA Medical Center > >>> 10 North Greene Street > >>> GRECC (BT/18/GR) > >>> Baltimore, MD 21201-1524 > >>> > >>> (Phone) 410-605-7119 > >>> (Fax) 410-605-7913 (Please call phone number above prior to faxing) > >>> [EMAIL PROTECTED] > >>> Confidentiality Statement: > >>> This email message, including any attachments, is for ...{{dropped:13}} > >>> > >> > >> ______________________________________________ > >> R-help@r-project.org 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. > >> > > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org 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. > > Confidentiality Statement: > This email message, including any attachments, is for ...{{dropped:10}} ______________________________________________ R-help@r-project.org 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.
