# [R] aggregate wind direction data with wind speed required

Bill Dunlap w||||@mwdun|@p @end|ng |rom gm@||@com
Sat May 13 22:38:51 CEST 2023

```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
> ---Oo---------oO----------------------------------------
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