#' Function to return the MH27 hydrologic indicator statistic for a given data frame
#'
#' This function accepts a data frame that contains a column named "discharge" and
#' calculates MH27. High peak flow. Compute the average peak flow value for flow events above a
#' threshold equal to the 75th percentile value for for the entire record. MH27 is the average peak flow divided by
#' the median flow for the entire record.
#'
#' @param qfiletempf data frame containing a "discharge" column containing daily flow values
#' @return mh27 numeric value of the mean daily flow for the given data frame
#' @export
#' @examples
#' load_data<-paste(system.file(package="HITHATStats"),"/data/obs_data.csv",sep="")
#' qfiletempf<-read.csv(load_data)
#' mh27(qfiletempf)
mh27 <- function(qfiletempf) {
isolateq <- qfiletempf$discharge
sortq <- sort(isolateq)
frank75 <- floor(findrank(length(sortq),0.25))
hfcrit75 <- sortq[frank75]
noyears <- aggregate(qfiletempf$discharge, list(qfiletempf$wy_val),
FUN = median, na.rm=TRUE)
colnames(noyears) <- c("Year", "momax")
noyrs <- length(noyears$Year)
peak <- rep(0,nrow(qfiletempf))
nevents <- 1
for (i in 1:noyrs) {
subsetyr <- subset(qfiletempf, as.numeric(qfiletempf$wy_val) == noyears$Year[i])
flag <- 0
peak[i] <- 0
for (j in 1:nrow(subsetyr)) {
if (subsetyr$discharge[j]>hfcrit75) {
flag <- flag+1
temp <- subsetyr$discharge[j]
nevents <- ifelse(flag==1,nevents+1,nevents)
peak[nevents] <- ifelse(temp>peak[nevents],temp,peak[nevents])
} else {flag <- 0}
}
}
peak_sub <- subset(peak,peak>0)
meanex <- mean(peak_sub)
mh27 <- meanex/ma2(qfiletempf)
return(mh27)
}
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