[R] apply, t-test and p-values

[David Winsemius]

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 <jsorkin at grecc.umaryland.edu 
> >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)
>> jsorkin at grecc.umaryland.edu
>> Confidentiality Statement:
>> This email message, including any attachments, is for ...{{dropped: 
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>
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