R/ra8.9.R

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

#' Function to return the RA8 and RA9 hydrologic indicator statistics for a given data frame
#' 
#' This function accepts a data frame that contains a column named "discharge" and calculates 
#' RA8; Number of reversals. Compute the number of days in each year when the change in flow from one day to the 
#' next changes direction. RA8 is the average (or median - Use Preference option) of the yearly values (days-temporal).
#' RA9; Variability in reversals. Compute the standard deviation for the yearly reversal values. RA9 is 100 times the 
#' standard deviation divided by the mean (percent-spatial).
#' 
#' @param qfiletempf data frame containing a "discharge" column containing daily flow values
#' @return ra8.9 list containing RA8 and RA9 for the given data frame
#' @export
#' @examples
#' qfiletempf<-sampleData
#' ra8.9(qfiletempf)
ra8.9 <- function(qfiletempf) {
  noyears <- data.frame(unique(qfiletempf$wy_val),stringsAsFactors=FALSE)
  colnames(noyears) <- c("wy_val")
  noyrs <- nrow(noyears)
  for (j in 1:noyrs) {
    subq <- subset(qfiletempf,qfiletempf$wy_val==noyears$wy_val[j])
    counter <- 0
    sub_length <- nrow(subq)-1
    for (i in 1:sub_length) {
      temp <- subq$discharge[i+1] - subq$discharge[i]
      if (i==1) {
        flag <- 0
        if (temp>0) flag<-1
        if (temp<0) flag<-2
      }
      if (i>1 && temp>0) {
        if (flag==2) counter <- counter+1
        flag <- 1
      }
      if (i>1 && temp<0) {
        if (flag==1) counter <- counter+1
        flag <- 2
      }
    }
    noyears$cnt[j] <- counter
  }
  ra8 <- mean(noyears$cnt)
  sd_diff <- sd(noyears$cnt)
  ra9 <- (sd_diff*100)/ra8
  ra8.9 <- list(ra8=ra8,ra9=ra9)
  return(ra8.9)
}