R/swe_to_melt.R

In hydroToolkit: Hydrological Tools for Handling Hydro-Meteorological Data from Argentina and Chile

#' Snow water equivalent to melt
#' 
#' @description Converts a snow water equivalent series (from snow pillow) into a melt series.
#'
#' @param df data frame with 'swe' serie in the second column. See \code{'read_XXX'} functions. 
#'
#' @return Data frame containing the numeric vector with melted snow. 
#' 
#' @export
#'
#' @examples
#' # Relative path to raw data
#' full_path <- system.file('extdata', package = "hydroToolkit")
#' 
#' # Read swe sheet
#' toscas_swe <- read_DGI(file = 'Toscas.xlsx', sheet = 'swe',
#'                 colName = 'swe(mm)', path = full_path)
#'
#' # swe to melt
#' toscas_melt <- swe_to_melt(df = toscas_swe)               
#'                 
swe_to_melt <- function(df) {
  #********************************
  # Condicionales
  #********************************
  # data.frame
  if(is.data.frame(df) == FALSE){
    return('df argument must be a data frame')
  }
  
  # numeric
  if(is.numeric(df[ , 2]) == FALSE){
    return('df column 2 must be numeric')
  }
  
  #********************************
  #********************************
  
  x <- df[ , 2]
  
  aux <- diff(x)
  aux <- ifelse(aux < 0 , aux, 0)
  
  out <- abs( c(0, aux) )
  
  df_out <- data.frame(df[ , 1], out)
  colnames(df_out) <- c('Date', 'Melt')
  
  return(df_out)
}