R/RProjects/HITHATStats/R/fh10.R

In jlthomps/EflowStats: Returns HIT/HAT Hydrologic Indicator stats for a given set of data

#' Function to return the FH10 hydrologic indicator statistic for a given data frame
#' 
#' This function accepts a data frame that contains a column named "discharge" and 
#' calculates the average number of annual flow events above a threshold (the median of the annual minima) for the entire record
#' 
#' @param qfiletempf data frame containing a "discharge" column containing daily flow values
#' @param pref string containing a "mean" or "median" preference
#' @return fh10 numeric value of average annual flow events above a threshold for the given data frame
#' @export
#' @examples
#' load_data<-paste(system.file(package="HITHATStats"),"/data/obs_data.csv",sep="")
#' qfiletempf<-read.csv(load_data)
#' fh10(qfiletempf)
fh10 <- function(qfiletempf, pref = "mean") {
  minbyyear <- aggregate(qfiletempf$discharge,list(qfiletempf$wy_val),FUN=min,na.rm=TRUE)
  medmin <- median(minbyyear$x)
  noyears <- aggregate(qfiletempf$discharge, list(qfiletempf$wy_val), 
                       FUN = median, na.rm=TRUE)
  colnames(noyears) <- c("Year", "momax")
  noyrs <- length(noyears$Year)
  hfcountbyyrfh4 <- rep(0, noyrs)
  for (i in 1:noyrs) {
    subsetyr <- subset(qfiletempf, as.numeric(qfiletempf$wy_val) == noyears$Year[i])
    flag <- 0
    for (j in 1:nrow(subsetyr)) {
      if (subsetyr$discharge[j]>medmin) {
        flag <- flag+1
        hfcountbyyrfh4[i] <- ifelse(flag==1,hfcountbyyrfh4[i]+1,hfcountbyyrfh4[i])
      } else {flag<-0}
    }
  }
  if (pref == "median") {
    fh10 <- median(hfcountbyyrfh4)
  }
  else {
    fh10 <- mean(hfcountbyyrfh4)
  }
  return(fh10)
}