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

[John Sorkin]

Jorge, David,
Thank you for a brilliant solution to my problem!
Thanks
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" <jorgeivanvelez at gmail.com> 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 <dwinsemius at comcast.net>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 <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 
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>>>
>>
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>>
>
>

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