How can I calculate wind direction average in R?

Question

I have a data set which consist of wind direction vector, as follows:

wdir <- c(296.9, 215.2, 204.8, 110.8, 287.6, 203.4, 253.1, 46.0, 298.8,  62.8, 183.4, 62.3,
          44.3, 97.6, 78.6, 125.6, 116.9, 121.0, 111.2, 335.8, 287.4, 51.7, 232.6, 265.5,
          269.7, 20.5, 17.0, 310.8)

Scalar values are in degrees.

How can I calculate mean wind direction?

Answer 1

This can be done using the circular package.

To get the mean of 45 and 315 you can use:

library(circular)
mean(circular(c(pi/4,7*pi/4)))
#Circular Data: 
#Type = angles 
#Units = radians 
#Template = none 
#Modulo = asis 
#Zero = 0 
#Rotation = counter 
#[1] -1.570092e-16

The reason it isn't exactly 0 is because of floating point precision in R.

To get the mean of wdiryou can use:

mean(circular(wdir, units = "degrees"))
#Circular Data: 
#Type = angles 
#Units = degrees 
#Template = none 
#Modulo = asis 
#Zero = 0 
#Rotation = counter 
#[1] 41.05411

Another example:

mean(circular(c(7*pi/2,pi/4, pi/2, 7*pi/2 )))
#Circular Data: 
#Type = angles 
#Units = radians 
#Template = none 
#Modulo = asis 
#Zero = 0 
#Rotation = counter 
#[1] -0.3926991