[R] aggregate wind direction data with wind speed required

[Jeff Newmiller]

You don't have to bother with the subtracting from pi/2 bit ... just assume the cartesian complex values are (y,x) instead of (x,y).

On May 13, 2023 1:38:51 PM PDT, Bill Dunlap <williamwdunlap using gmail.com> wrote:
>I think that using complex numbers to represent the wind velocity makes
>this simpler.  You would need to write some simple conversion functions
>since wind directions are typically measured clockwise from north and the
>argument of a complex number is measured counterclockwise from east.  E.g.,
>
>windToComplex <-
>function(speed, degreesCW) {
>  complex(mod=speed, arg=(90-degreesCW)/180*pi)
>}
>complexToWind <-
>function(z) {
>  # Convert complex velocity z to speed and direction (degrees clockwise
>  # from north, in range [0,360)).
>  stopifnot(is.complex(z))
>  data.frame(speed = Mod(z), degreesCW = (pi - Arg(z*1i))/(2*pi)*360)
>}
>
>Then use FUN=mean instead of my_fun.
>
>-Bill
>
>On Sat, May 13, 2023 at 7:51 AM Stefano Sofia <
>stefano.sofia using regione.marche.it> wrote:
>
>> Dear list users,
>>
>> I have to aggregate wind direction data (wd) using a function that
>> requires also a second input variable, wind speed (ws).
>>
>> This is the function that I need to use:
>>
>>
>> my_fun <- function(wd1, ws1){
>>
>>   u_component <- -ws1*sin(2*pi*wd1/360)
>>   v_component <- -ws1*cos(2*pi*wd1/360)
>>   mean_u <- mean(u_component, na.rm=T)
>>   mean_v <- mean(v_component, na.rm=T)
>>   mean_wd <- (atan2(mean_u, mean_v) * 360/2/pi) + 180
>>   result <- mean_wd
>>   result
>> }
>>
>> Does the aggregate function work only with functions with a single input
>> variable (the one that I want to aggregate), or its use can be extended to
>> functions with two input variables?
>>
>> Here a simple example (which is meaningless, the important think is the
>> concept behind it):
>> df <- data.frame(day=c(1, 1, 1, 2, 2, 2, 3, 3), month=c(1, 1, 2, 2, 2, 2,
>> 2, 2), wd=c(45, 90, 90, 135, 180, 270, 270, 315), ws=c(7, 7, 8, 3, 2, 7,
>> 14, 13))
>>
>> aggregate(wd ~ day + month, data=df, FUN = my_fun)
>>
>> cannot work, because ws is not taken into consideration.
>>
>> I got lost. Any hint, any help?
>> I hope to have been able to explain my problem.
>> Thank you for your attention,
>> Stefano
>>
>>
>>          (oo)
>> --oOO--( )--OOo--------------------------------------
>> Stefano Sofia PhD
>> Civil Protection - Marche Region - Italy
>> Meteo Section
>> Snow Section
>> Via del Colle Ameno 5
>> 60126 Torrette di Ancona, Ancona (AN)
>> Uff: +39 071 806 7743
>> E-mail: stefano.sofia using regione.marche.it
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-- 
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