[R] newbie question: p.values in a column

[Emmanuel Paradis]

At 07:48 18/09/02 -0500, Hao Chen wrote:
>Hello,
>
>I have a vector (v) with 6 columns and 2000 rows. I am trying to do one 

So v is a matrix (not a vector).

>sample t.test for each row (I know this sounds crazy) and put the 
>p.values into the 7th column.
>
>I know I can access the p.value via t.test(v[i,])[3]$p.value; I know I 

The index `[3]' is useless here. You can use either `[3]' or `$p.value',
but there is a difference between them:

> str(t.test(1:10)[3])
List of 1
 $ p.value: num 0.000278
> str(t.test(1:10)$p.value)
 num 0.000278

>can do t.test on the row by apply(v, 1, t.test), but I just couldn't 
>figure out how to fit them together.

I guess there are several solutions. Here is mine.

N <- nrow(v)
PVAL <- numeric(N)
for (i in 1:N) PVAL[i] <- t.test(v[i, ])$p.value
v <- cbind(v, PVAL)


Hoping this helps.

EP

>I'd very appreciate your help!!
>
>Hao Chen
>
>
>
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