R help - Aug 2006 - CircStats help

Hello,

	I am quite new to R and although I have read some material  
(apparently not enough) I'm getting very frustrated. I'm trying to do  
some simple circular statistics in R (CircStats, primarily circ.mean)  
and I'm confused about the results. What is a negative radian or  
degree mean in R? I thought it would be a coterminal angle, but that  
doesn't make sense with my data points. I'm sorry if this is trivial  
to most of you, but I really appreciate any help.

I have tried to obtain the book this package was based on  
(Jammalamadaka and SenGupta 2001 Topics in Circular Statistics) but  
it is not available at any of my university libraries.

Here is an example. The values of "x" are directions in degrees of  
one amphibian over 6 days and I'd just like to simply calculate the  
mean direction:

 > x <- c(5.009684,37.814266, 295.722970, 0.000000,  
326.463366,242.678840)
 > radx <- rad(x)
 > circ.mean(radx)
[1] -0.4283351
 > deg(-0.4283351)
[1] -24.54179

I would just like this number to be converted to the appropriate  
angle between 0-360 degrees. Can someone help me?

Sincerely,

Isabelle Deguise
MSc candidate





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Isabelle Deguise <ideguise <at> interchange.ubc.ca> writes:
> 
> Hello,
> 
> 	
>  > x <- c(5.009684,37.814266, 295.722970, 0.000000,  
> 326.463366,242.678840)
>  > radx <- rad(x)
>  > circ.mean(radx)
> [1] -0.4283351
>  > deg(-0.4283351)
> [1] -24.54179
> 
> I would just like this number to be converted to the appropriate  
> angle between 0-360 degrees. Can someone help me?
> 
  Just add 360 to the result ... when in doubt, you can also look at what
the function is actually doing by typing the name of the
function by itself, e.g.
> circ.mean
In this case it shows that the function is just adding
up the sines and cosines of the individual angles and
then taking the arc-tangent.  With this size problem
you can work through the details and understand how
it all works ...

  Ben Bolker