R/metar_pressure.R

In pmetar: Processing METAR Weather Reports

#' Get atmospheric pressure.
#'
#' Extract and parse an air pressure value from METAR weather report.
#'
#' @param x character vector; a METAR weather report or reports.
#' @param altimeter boolean; if FALSE, the default value, a pressure is returned in hPa,
#' if TRUE a pressure is returned in inHg (inch of mercury).
#' @param check logical; if TRUE the syntax of METAR reports will be checked.
#'
#' @return a numeric vector with air pressure in inHg or hPa.
#'
#' @export
#'
#' @examples
#' metar_pressure("EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG")
#' metar_pressure("CYUL 281800Z 13008KT 30SM BKN240 01/M06 A3005", altimeter = TRUE)
#' metar_pressure("201711271930 METAR LEMD 271930Z 02002KT CAVOK 04/M03 Q1025 NOSIG= NOSIG=")
#'
metar_pressure <- function(x, altimeter = FALSE, check = FALSE){
  # check if x is a data frame
  if(is.data.frame(x)){
    stop("pmetar package error: Invalid input format! Argument is not an atomic vector.", call. = FALSE)
  }
  if(!altimeter){
    cf_hPa <- 1
    cf_inHg <- 0.3386389
  } else {
    cf_hPa <- 0.0295333727
    cf_inHg <- 0.01
  }
  out <- c(1:length(x))
  out[c(1:length(x))] <- NA
  # Remove part after RMK
  x <- stringr::str_split_fixed(x, pattern = "RMK", n = 2)[,1]
  # Remove part after TEMPO
  x <- stringr::str_split_fixed(x, pattern = "TEMPO", n = 2)[,1]
  # check syntax
  if (check) {
    icorrect <- metar_is_correct(x)
  } else {
    icorrect <- rep(TRUE, length(x))
  }
  x <- x[which(icorrect)]
  outx <- c(1:length(x))
  outx[c(1:length(x))] <- NA
  fP <- stringr::str_detect(x, pattern = "\\sQ\\d{4}")
  outx[fP] <- round(as.numeric(stringr::str_sub(stringr::str_extract(x[fP], pattern = "\\sQ\\d{4}"), 3, 6)) * cf_hPa, 2)
  fP <- stringr::str_detect(x, pattern = "\\sA\\d{4}")
  outx[fP] <- round(as.numeric(stringr::str_sub(stringr::str_extract(x[fP], pattern = "\\sA\\d{4}"), 3, 6)) * cf_inHg, 2)
  out[which(icorrect)] <- outx
  out
}