R/day.dist.R

In nickbond/hydrostats: Hydrologic Indices for Daily Time Series Data

day.dist <- function(Dates = NULL, days = NULL, years = NULL) {
    
    if (any(class(Dates) == "POSIXct") | any(class(Dates) == "Date") == T) {
        
        days <- as.numeric(strftime(Dates, format = "%j"))
        years <- as.numeric(strftime(Dates, format = "%Y"))
        
    } else {
        days <- days
        years <- years
    }
    
    
    year.length <- get.days(years)
    theta <- c()
    adjust <- 0.5 * ((2 * pi)/365)
    theta <- days * (2 * pi/year.length) - adjust
    x <- mean(cos(theta))
    y <- mean(sin(theta))
    m.theta <- atan2(y, x)
    m.deg <- (m.theta * 365/(2 * pi)) + 0.5
    if (m.deg < 0) 
        m.deg <- m.deg + 365
    
    
    r <- sqrt((x^2) + (y^2))
    sd.rad <- sqrt(-2 * log(r))
    sd.deg <- sd.rad * (365/(2 * pi))
    
    
    data.frame(mean.doy = round(m.deg, 0), sd.doy = round(sd.deg, 0))
    
}