#' Function to return the TA3 hydrologic indicator statistic for a given data frame
#'
#' This function accepts a data frame that contains a column named "discharge" and threshold value obtained
#' using the peakdata and peakthresh functions and calculates
#' TA3; Seasonal predictability of flooding. Divide years up into 2-month periods (that is, Oct-Nov, Dec-Jan,
#' and so forth). Count the number of flood days (flow events with flows > 1.67-year flood) in each period over
#' the entire flow record. TA3 is the maximum number of flood days in any one period divided by the total number
#' of flood days (dimensionless-temporal).
#'
#' @param qfiletempf data frame containing a "discharge" column containing daily flow values
#' @param thresh numeric containing 1.67-year flood threshold calculated by getPeakThresh
#' @return ta3 numeric containing TA3 for the given data frame
#' @export
#' @examples
#' qfiletempf<-sampleData
#' ta3(qfiletempf, 1158)
ta3 <- function(qfiletempf, thresh) {
lfcrit <- thresh
nomonyears <- aggregate(qfiletempf$discharge, list(qfiletempf$wy_val,qfiletempf$month_val),
FUN = median, na.rm=TRUE)
colnames(nomonyears) <- c("Year","month", "momax")
nomonyrs <- nrow(nomonyears)
dur <- data.frame(Year = rep(0,nrow(nomonyears)), month = rep(0,nrow(nomonyears)), dur = rep(1,nrow(nomonyears)))
for (i in 1:nomonyrs) {
monyears <- nomonyears[i,]
colnames(monyears) <- c("wy_val","month_val","momax")
subsetyr <- merge(qfiletempf,monyears,by = c("wy_val","month_val"))
flag <- 0
nevents <- 0
for (j in 1:nrow(subsetyr)) {
if (subsetyr$discharge[j]>lfcrit) {
flag <- flag+1
nevents <- ifelse(flag==1,nevents+1,nevents)
dur$Year[i] <- subsetyr$wy_val[j]
dur$month[i] <- subsetyr$month_val[j]
dur$dur[i] <- nevents
} else {flag <- 0}
}
}
dur$season <- ifelse(as.numeric(dur$month)==10,10,ifelse(as.numeric(dur$month)==11,10,ifelse(as.numeric(dur$month)==12,12,ifelse(as.numeric(dur$month)==1,12,ifelse(as.numeric(dur$month)==2,2,ifelse(as.numeric(dur$month)==3,2,ifelse(as.numeric(dur$month)==4,4,ifelse(as.numeric(dur$month)==5,4,ifelse(as.numeric(dur$month)==6,6,ifelse(as.numeric(dur$month)==7,6,ifelse(as.numeric(dur$month)==8,8,ifelse(as.numeric(dur$month)==9,8,99))))))))))))
dur <- dur[!dur$season==99,]
num_season <- aggregate(dur$dur, list(dur$season), sum)
ta3 <- max(num_season$x)/sum(num_season$x)
return(ta3)
}
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