From: Michael Peckford <michael.peckford_at_acadiau.ca>

Date: Wed 29 Jun 2005 - 03:34:33 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Jun 29 03:37:42 2005

Date: Wed 29 Jun 2005 - 03:34:33 EST

Hi, a question about the circular mean function in the package CircStats:

Can anyone shed some light on why the circ mean function seems to make sense for the first 2 set of bearings and then the mean of 225 and 45 degrees gives an unexpected 180 deg.

> deg(circ.mean(c(rad(222),rad(45))))%%360

[1] 133.5

> deg(circ.mean(c(rad(224),rad(45))))%%360

[1] 134.5

> deg(circ.mean(c(rad(225),rad(45))))%%360

[1] 180

> deg(circ.mean(c(rad(226),rad(45))))%%360

[1] 315.5

Can anyone explain this???

This problem was first detected when I was trying to take the circ weighted means of my data:

With 2 groups of bearings:

x <- c(270,180)

y <- c(45,270)

the circular mean of these bearings gives:

> deg(circ.mean(c(rad(x),rad(y))))%%360

[1] 257.2356

When finding the weighted means I get this:

> meany <- circ.mean(rad(y))

> meanx <- circ.mean(rad(x))

> deg(circ.weighted.mean(c(meanx,meany),c(2,2)))%%360

[1] 281.25

The function for weighted mean I am using:

circ.weighted.mean <- function (x,w)

{

sinr <- sum(w*sin(x))

cosr <- sum(w*cos(x))

circmean <- atan(sinr, cosr)

circmean

}

I am assuming that the problem that mention above is the cause of the different mean bearings.

Am I missing something fundamental here?

Thanks,

Mike

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Jun 29 03:37:42 2005

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