I'd suggest looking at the boxcox function in the MASS package, which might
show you how to change your code.
It would be easier to diagnose the problem if you included a small example
showing the errors. Some possibilities are that if x is a vector, nrow(x)
will return NULL, that you are using lambda as the index variable in the
for loop, so the sequence generated in the second line is getting
overwritten, and the for loop isn't enclosed in braces, so only the first
line will be counted as being in the loop.
HTH,
David
On 11/10/06, Dale Steele <[EMAIL PROTECTED]> wrote:
>
> I'm trying to write a small function (below) to compute Box & Cox
> transformations of x for arbitrary values of lambda. I'd like to
> specify a range of values for lamba (min,max,step) and am having trouble
> getting the for loop to work. Suggestions?
>
> Any pointers to resources for learning to write functions in R for
> neophyte programmers? Thanks. --Dale
>
>
> boxcox <- function(x,min,max,step) {
> lambda <- seq(min,max,step)
> s <- length(lambda)
> for (lambda in 1:s)
> n <- nrow(x)
> if(lambda ==0) xL <- log(x) else
> xL <- ((x^lambda) - 1)/lambda
> xLbar <- mean(xL)
> t1 <- (-n/2)* log((1/n)*sum((xL - xLbar)^2))
> t2 <- (lambda - 1)*sum(log(x))
> l= t1 + t2
> l
> }
>
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--
=================================
David Barron
Said Business School
University of Oxford
Park End Street
Oxford OX1 1HP
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