[R] help on understanding a code

[Mike Lawrence]

You haven't provided us enough information. You should also provide
examples where we can access all the called objects; for example,
ttest() is not a built-in function, so we have no idea what it is.
Same goes for dat and y.

On Tue, Jun 2, 2009 at 11:43 AM, Hongyuan Cao <hongyuancao at gmail.com> wrote:
> Dear R user,
>
> I am trying to understand this following code. Basically it's using a
> permutation method to calculate p value. But I would like to know exactly
> how the permutation works.
>
> #calculates null statistics
> tt0 <- 0
> set.seed(123)
> B <- 100
> for(i in 1:B) {
> v <- sample(y)
> tt0 <- c(tt0,ttest(dat,v)$tt)
> }
> tt0 <- tt0[-1]
> #form p-values
> att <- abs(tt)
> att0 <- abs(tt0)
> v <- c(rep(T,m),rep(F,m*B))
> v <- v[rev(order(c(att,att0)))]
> u <- 1:length(v)
> w <- 1:m
> p <- (u[v==TRUE]-w)/(B*m)
> p <- p[rank(-att)]
>
> For some reason, I couldn't get any results for p. Maybe R encoded T and F
> to corresponding numerical ones.
>
> Any idea?
>
> Thanks,
> Hongyuan
>
>        [[alternative HTML version deleted]]
>
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>



-- 
Mike Lawrence
Graduate Student
Department of Psychology
Dalhousie University

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