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#' Get wind speed
#'
#' Extract a wind speed value from METAR weather report.
#'
#' @param x character vector; METAR weather report or reports.
#' @param metric logical; the default value is TRUE and a returned wind speed is in m/s;
#' if it's FALSE then in knots.
#' @param check logical; the default value is FALSE, if METAR report fails the syntax
#' check, NA value will be returned. If FALSE, zero values will be returned for
#' METAR reports with incorrect syntax.
#'
#' @return a numeric vector. A wind speed in m/s or in knots.
#'
#' @export
#'
#' @examples
#' metar_speed("EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG")
#' metar_speed("CYUL 281800Z 13008KT 30SM BKN240 01/M06 A3005 RMK CI5 SLP180", metric = FALSE)
#' metar_speed("201711271930 METAR LEMD 271930Z 02002KT CAVOK 04/M03 Q1025 NOSIG= NOSIG=")
#' metar_speed("EPKK 141730Z VRB01KT CAVOK 21/16 Q1028")
#'
metar_speed <- function(x, metric = TRUE, 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)
}
# define conversion coefficients
if(metric){
cfm <- 1
cfi <- 0.5144447
} else {
cfm <- 1/0.5144447
cfi <- 1
}
out <- rep(NA, length(x))
# 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
fMPS <- stringr::str_detect(x, pattern = "(\\d{5}(MPS|G\\d{2}MPS)|VRB\\d{2}MPS|VRB[\\d]+G[\\d]+KT|VRB[\\d]+G[\\d]+MPS)")
fKT <- stringr::str_detect(x, pattern = "(\\d{5}(KT|G\\d{2}KT)|VRB\\d{2}KT|VRB[\\d]+G[\\d]+KT|VRB[\\d]+G[\\d]+MPS)")
outx[fMPS] <- as.numeric(stringr::str_sub(stringr::str_extract(x[fMPS],
pattern = "(\\d{5}(MPS|G\\d{2}MPS)|VRB\\d{2}MPS|VRB[\\d]+G[\\d]+KT|VRB[\\d]+G[\\d]+MPS)")
, 4, 5)) * cfm
outx[fKT] <- as.numeric(stringr::str_sub(stringr::str_extract(x[fKT],
pattern = "(\\d{5}(KT|G\\d{2}KT)|VRB\\d{2}KT|VRB[\\d]+G[\\d]+KT|VRB[\\d]+G[\\d]+MPS)")
, 4, 5)) * cfi
fMPS <- stringr::str_detect(x, pattern = "\\d{3}P49MPS")
fKT <- stringr::str_detect(x, pattern = "\\d{3}P99KT")
if (metric) {
outx[fMPS] <- 50
outx[fKT] <- 50
} else {
outx[fMPS] <- 100
outx[fKT] <- 100
}
out[which(icorrect)] <- outx
out
}
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