# R/th1.2.R In jlthomps/EflowStats: Returns HIT/HAT Hydrologic Indicator stats for a given set of data

#### Documented in th1.2

```#' Function to return the TH1 and TH2 hydrologic indicator statistics for a given data frame
#'
#' This function accepts a data frame that contains a column named "discharge" and calculates
#' TH1; Julian date of annual maximum. Determine the Julian date that the maximum flow occurs for each year.
#' Transform the dates to relative values on a circular scale (radians or degrees). Compute the x and y components
#' for each year and average them across all years. Compute the mean angle as the arc tangent of y-mean divided by
#' x-mean. Transform the resultant angle back to Julian date (Julian day-spatial). and
#' TH2; Variability in Julian date of annual maxima. Compute the coefficient of variation for the mean x and y
#' components and convert to a date (Julian days-spatial).
#'
#' @param qfiletempf data frame containing a "discharge" column containing daily flow values
#' @return th1.2 list containing TH1 and TH2 for the given data frame
#' @export
#' @examples
#' qfiletempf<-sampleData
#' th1.2(qfiletempf)
th1.2 <- function(qfiletempf) {
max1daybyyear <- aggregate(qfiletempf\$discharge,
list(qfiletempf\$wy_val), max, na.rm=TRUE)
colnames(max1daybyyear) <- c("wy_val","discharge")
qfiletempf\$wy_day_val <- ifelse(qfiletempf\$jul_val>=274,qfiletempf\$jul_val-273,qfiletempf\$jul_val+92)
maxjulbyyear <- aggregate(qfiletempf\$wy_day_val, list(qfiletempf\$wy_val,qfiletempf\$discharge),min,na.rm=TRUE)
colnames(maxjulbyyear) <- c("wy_val","discharge","jul_val")
maxjulday <- merge(maxjulbyyear,max1daybyyear,by = c("wy_val","discharge"))
maxjulday\$jul_val <- ifelse(maxjulday\$jul_val<=92,maxjulday\$jul_val+274,maxjulday\$jul_val-92)
maxjulday\$np <- cos(maxjulday\$jul_val*2*pi/365.25)
maxjulday\$mdata <- sin(maxjulday\$jul_val*2*pi/365.25)
xbar <- mean(maxjulday\$np)
ybar <- mean(maxjulday\$mdata)
if (xbar>0) {
th1_temp <- atan(ybar/xbar)*180/pi
} else if (xbar<0) {
th1_temp <- (atan(ybar/xbar)*180/pi)+180
} else if (xbar==0 && ybar>0) {
th1_temp <- 90
} else if (xbar==0 && ybar<0) {
th1_temp <- 270
}
th1_temp <- ifelse(th1_temp<0,th1_temp+360,th1_temp)
th1 <- th1_temp*365.25/360
th2_a <- sqrt((xbar*xbar)+(ybar*ybar))
th2_b <- sqrt(2*(1-th2_a))
th2 <- th2_b*180/pi/360*365.25
th1.2<-list(th1=th1,th2=th2)
return(th1.2)
}
```
jlthomps/EflowStats documentation built on May 19, 2019, 12:48 p.m.