#' Function to return the FH6 hydrologic indicator statistic for a given data frame
#'
#' This function accepts a data frame that contains a column named "discharge" and calculates
#' FH6; Flood frequency. Compute the average number of flow events with flows above a threshold equal to three
#' times the median flow value for the entire flow record. FH6 is the average (or median-Use Preference option)
#' number of events (number of events/year-temporal).
#'
#' @param qfiletempf data frame containing a "discharge" column containing daily flow values
#' @param pref string containing a "mean" or "median" preference
#' @return fh6 numeric value of FH6 for the given data frame
#' @export
#' @examples
#' qfiletempf<-sampleData
#' fh6(qfiletempf)
fh6 <- function(qfiletempf, pref = "mean") {
hfcrit <- 3*ma2(qfiletempf)
noyears <- aggregate(qfiletempf$discharge, list(qfiletempf$wy_val),
FUN = median, na.rm=TRUE)
colnames(noyears) <- c("Year", "momax")
noyrs <- length(noyears$Year)
counter <- rep(0,noyrs)
for (i in 1:noyrs) {
subsetyr <- subset(qfiletempf, as.numeric(qfiletempf$wy_val) == noyears$Year[i])
flag <- 0
counter[i] <- 0
for (j in 1:nrow(subsetyr)) {
if (subsetyr$discharge[j]>hfcrit) {
flag <- flag+1
counter[i] <- ifelse(flag==1,counter[i]+1,counter[i])
} else {flag <- 0}
}}
if (pref == "median") {
fh6 <- median(counter)
}
else {
fh6 <- mean(counter)
}
return(fh6)
}
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