**From:** Andrew C. Ward (*s195404@student.uq.edu.au*)

**Date:** Thu 24 Apr 2003 - 13:17:57 EST

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Message-id: <1051154277.3ea757654bbb4@my.uq.edu.au>

I have written the following function to calculate the weighted mean

difference for univariate data (see

http://www.xycoon.com/gini_mean_difference.htm for a related

formula). Unsurprisingly, the function is slow (compared to sd or mad)

for long vectors. I wonder if there's a way to make the function

faster, short of creating an external C function. Thanks very much

for your advice.

gmd <- function(x, w) { # x=data vector, w=weights vector

n <- length(x)

tmp <- 0

for (i in 1:n) {

for (j in 1:n) {

tmp <- tmp + w[i]*abs(x[i]-x[j])

}

}

retval <- 0.5*sqrt(pi)*tmp/((n-1)*sum(w))

}

gmd(rnorm(100))

Regards,

Andrew C. Ward

CAPE Centre

Department of Chemical Engineering

The University of Queensland

Brisbane Qld 4072 Australia

andreww@cheque.uq.edu.au

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**Next message:**Deepayan Sarkar: "Re: [R] Fast R implementation of Gini mean difference"**Previous message:**Tony Plate: "RE: [R] sum"**Next in thread:**Deepayan Sarkar: "Re: [R] Fast R implementation of Gini mean difference"**Reply:**Deepayan Sarkar: "Re: [R] Fast R implementation of Gini mean difference"**Maybe reply:**DJNordlund@aol.com: "Re: [R] Fast R implementation of Gini mean difference"**Reply:**Adelchi Azzalini: "Re: [R] Fast R implementation of Gini mean difference"**Reply:**Adelchi Azzalini: "Re: [R] Fast R implementation of Gini mean difference"**Maybe reply:**Andrew C. Ward: "RE: [R] Fast R implementation of Gini mean difference"

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