Sorry for the big delay of my report, but prolonged severe weather conditions
often absorb a large amount of time and energies to my studies.
Thanks to all of you for your suggestions.
I have not been able to implement Bert Gunter's hint, his code gave me an error
I have not been able to fix.
Bill Dunlap's hint is smart and has been resolutive.
Thank you again to all of you
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.so...@regione.marche.it
---Oo---------oO----------------------------------------
________________________________
Da: Bill Dunlap <williamwdun...@gmail.com>
Inviato: sabato 13 maggio 2023 22:38
A: Stefano Sofia
Cc: r-help@R-project.org
Oggetto: Re: [R] aggregate wind direction data with wind speed required
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.so...@regione.marche.it<mailto:stefano.so...@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.so...@regione.marche.it<mailto:stefano.so...@regione.marche.it>
---Oo---------oO----------------------------------------
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