How to extract x rows to get x pvalues using t.test

From: Adaikalavan Ramasamy

You will need to _apply_ the t-test row by row. 

   apply( genes, 1, function(x) t.test( x[1:2], x[3:4] )$p.value )

apply() is a C optimised version of for. Running the above code on a
dataset with 56000 rows and 4 columns took about 63 seconds on my 1.6
GHz Pentium machine with 512 Mb RAM. See help("apply") for 
more details.

Regards, Adai



On Tue, 2005-03-15 at 11:59 -0600, Jagarlamudi, Choudary wrote:

Hi all,
 
  My data
genes
     [,1] [,2] [,3] [,4]
[1,]   25   72   23   55
[2,]   34   53   41   33
[3,]   26   43   26   44
[4,]   36   64   64   22
[5,]   47   72   67   34

 stu<-t.test(genes[,1:2],genes[,3:4])

stu$p.value

[1] 0.4198002

i get 1 pvalue for the entire col1:col2  Vs col3:col4. I am 

trying to get 5 p values for the 5 rows i have.

I am trying to avoid a for loop coz my actual data has 

56000 rows and its taking more than 4 minutes to

compute.
 
Thanks in advance.
 
Choudary Jagarlamudi
Instructor
Southwestern Oklahoma State University
STF 254
100 campus Drive
Weatherford OK 73096
Tel 580-774-7136

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