R/U_period.R

In maibrittbergh/dischanalyst: Analyses Hydrological Data, especially Discharge Data

#' Max. Amount of Days under Threshold value U within Time Series
#'
#' @description Function indicates the longest that a certain value (U) was undercut (at a given measuring point of a given river),
#' within the entire time period of the measurements.
#'
#' @param U numeric; Limit Value. Function returns longest time measured under value U.
#' @param station character; Name of the Station e.g. "COCHEM" - must be named equally like list entry in data.
#' @param data list; Contains all stations that the discharge analysis should consider. List can be created by \link[dischanalyst]{grdc_list}. Each entry of the list contains the existing discharge measurements (as numeric) and the corresponding dates (as character) for the station.
#' @return Function returns longest time measured under value U in days.
#' @export
#'
#'
#' @examples
#' \dontrun{ U_period(88, "TRIER UP", mosel)}
#'
U_period=function(U, station, data){
  nbr=which(names(data)==station)
  Val=data[[nbr]][,2]
  uU=which(Val<U)
  l=length(uU)
  if (all(Val>U)) {paste("No days")}
  else {
    c=rep(0,l)#oder l-1
    for ( i in 1:l){
      c[i]=(uU[i+1]-uU[i])
    }
    index=cbind(c, uU)
    G=which(c>1)
    c[G]=0  #Vektor c in 0 und 1
    c[is.na(c)] = 0


    d=c
    l=length(c)
    e=rep(0,l)


    for (i in 2:l){
      e[1]=d[1]
      if ((e[i-1]+d[i]) > e[i-1]){e[i]=e[i-1]+d[i]}
      else {e[i]=0}
    }

    ic_max=which(e == (max(e)))
    id_End_period=index[,2][ic_max]
    id_Start_period=id_End_period-max(e)


    Startdate=data[[nbr]][,1][id_Start_period]
    Enddate=data[[nbr]][,1][id_End_period]

    paste("Length of maximum time period  under given Value of", U, " [m³/s] is", max(e), "days. Timeperiod from:",Startdate, "to:",Enddate)
  }

}