R/water_year_trim.R

In HARPgroup/cbp6:

#' Trimming Data to Water Year Function
#' @description Trims data to water year
#' @param data dataframe of date and flow data taken from import data functions
#' @return dataframe trimmed to water year
#' @import lubridate
#' @export water_year_trim

water_year_trim <- function(data) {
  data.length <- length(data$date)
  start.month <- month(data$date[1])
  end.month <- month(data$date[data.length])
  start.day <- day(data$date[1])
  end.day <- day(data$date[data.length])
  
  if (start.month <= 9) {
    start.year <- year(data$date[1])
  } else if (start.month == 10 & start.day == 1) {
    start.year <- year(data$date[1])
  } else {
    start.year <- year(data$date[1]) + 1
  }
  
  if (end.month >= 10) {
    end.year <- year(data$date[data.length])
  } else if (end.month == 9 & end.day == 30) {
    end.year <- year(data$date[data.length])
  } else {
    end.year <- year(data$date[data.length]) - 1
  }
  
  start.date <- paste0(start.year, "-10-01")
  end.date <- paste0(end.year, "-09-30")
  
  start.line <- which(data$date == start.date)
  end.line <- which(data$date == end.date)
  
  data <- data[start.line:end.line,]
  return(data)
}