R/deltaDaysForSameValue.R

In bvhest/KNMIr: functions for retrieving historic climate data and the six-day forecast from the Dutch meteorological institute KNMI

#' @title difference-in-days between to equivalent time series
#'
#' @description
#' \code{difference_in_days} determines the two dates in two ranges of values that have the
#' most similar value. Next, the difference between the two days is calculated.
#'
#' @details
#' this helper-function calculates the difference in days between the maximum value in the first range with daily values
#' and the day-of-the-year that this value occured in the second range with daily values. Normally the first range
#' contains the actual values and the second range contains a historic time series of data.
#' The function expects more or less continuously increasing values, for example the Huglin-index, VE-index, the yearly
#' totalized amount of rain, etc.
#'
#' @param ac dataframe containing the day-of-the-year and a column containing the value (note: The values must belong to the same year. The column-names are not relevant.)
#' @param ljg dataframe containing the day-of-the-year and a column containing the value (note: The values must belong to the same year. The column-names are not relevant)
#' @return difference in days between the two ranges with daily values.
#' @export

difference_in_days <- function(ac, ljg) {
  # check the provided data-frames:
  if (dim(ac)[2] > 2) {
    stop("The first data-frame has more than 2 columns. Please provide only the day-of-the-year and a column containing the value.")
  }
  if (dim(ljg)[2] > 2) {
    stop("The second data-frame has more than 2 columns. Please provide only the day-of-the-year and a column containing the value.")
  }
  if (dim(ac)[1] > 366) {
    stop("The first data-frame seems to contain data for more than one year.")
  }
  if (dim(ljg)[1] > 366) {
    stop("The second data-frame seems to contain data for more than one year.")
  }

  # rename the column-names
  colnames(ac) <- c("doy", "value")
  colnames(ljg) <- c("doy", "value")

  # perform the calculation
  DD.actueel <- max(ac$value)
  dvj.actueel <- ac[ac$value == DD.actueel, ]$doy
  dvj.ljgem <- as.integer(mean(ljg[ljg$value > DD.actueel - 5 & ljg$value < DD.actueel + 5, ]$doy))
  if (is.na(dvj.ljgem)) {
    (dvj.actueel - 365)
  } else {
    (dvj.actueel - dvj.ljgem)
  }
}