[R] Shapiro-Wilk cpoefficients: 2 Qs

[(Ted Harding)]

Greetings!
I want to have the coefficients that R uses in shapiro.test()
for the Shapiro-Wilk test for a prticular sample size, i.e.
the a[i] in

  W = Sum(a[i]*x[i])/(Sum(x[i] - mean(x))^2)

(where the x[i] are sorted). Two questions:

Q1:
Is there a readymade R function from which I can extract these?

Q2:
I was wondering if I might be able to modify the code for the
function shapiro.test() so as to obtain these. When I enter

  shapiro.test

I get:

function (x) 
{
    DNAME <- deparse(substitute(x))
    x <- sort(x[complete.cases(x)])
    stopifnot(is.numeric(x))
    n <- length(x)
    if (n < 3 || n > 5000) 
        stop("sample size must be between 3 and 5000")
    rng <- x[n] - x[1L]
    if (rng == 0) 
        stop("all 'x' values are identical")
    if (rng < 1e-10) 
        x <- x/rng
    n2 <- n%/%2L
    sw <- .C(R_swilk, init = FALSE, as.single(x), n, n1 = n, 
        n2, a = single(n2), w = double(1), pw = double(1), ifault = integer(1L))
    if (sw$ifault && sw$ifault != 7) 
        stop(gettextf("ifault=%d. This should not happen", sw$ifault), 
            domain = NA)
    RVAL <- list(statistic = c(W = sw$w), p.value = sw$pw, method =
"Shapiro-Wilk normality test", 
        data.name = DNAME)
    class(RVAL) <- "htest"
    return(RVAL)
}
<environment: namespace:stats>


So, on the off-chance that the variable 'sw' computed therein might
contain something useful, I changed "return(RVAL)" to "return(sw)",
just in case the coefficients might be lurking as a component of sw,
and used this to define a function SW_ted(). I then ran

  SW_ted(rnorm(30))
  # Error in SW_ted(rnorm(30)) : object 'R_swilk' not found

Since shapiro.test(rnorm(30)) works perfectly, and since the
"stats:" namespace is already present, I am wondering why
"object 'R_swilk' not found" when it clearly can be found by
shapiro.test().

So why is it that in the ".C" call:

  sw <- .C(R_swilk, ... )

my modifiction of shapiro.test() doesn't find it?

(No doubt there is some dumb oversight behind this, but I'd be
grateful to be told what it is)!

With thanks,
Ted.

-------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
Date: 04-Apr-2012  Time: 23:06:32
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