#' @title Traffic Speed Bands
#'
#' @description Returns traffic advisories about current traffic conditions that are displayed on EMAS signboards along expressways and major roads.
#'
#' @param api_key API key for LTA's Datamall
#' @return A dataframe containing each traffic advisory message and its coordinates
#' @examples
#' \donttest{
#' getVMS(mykey)
#' }
#' @import httr
#' @export getVMS
getVMS <- function(api_key) {
result <- httr::GET("http://datamall2.mytransport.sg/ltaodataservice/VMS",
httr::add_headers(AccountKey = api_key))
if (httr::http_status(result)$category != "Success") {
message("Unsuccessful API call for VMS/EMAS messages. Please check your parameters or connection.")
return(result)
} else {
message("Successful API call for VMS/EMAS messages. Processing page 1...")
}
output <- data.frame(matrix(nrow = 0, ncol = 4))
vms_list <- httr::content(result)[[2]]
for (i in 1:length(vms_list)) {
interim <- vms_list[[i]]
interim[sapply(interim, is.null)] <- 0
output <- rbind(output, t(unlist(interim)))
}
names(output) <- names(unlist(vms_list[[1]]))
num <- 2
while(length(vms_list) > 499) {
result <- httr::GET(paste("http://datamall2.mytransport.sg/ltaodataservice/VMS", "?$skip=", (num-1)*500, sep=""),
httr::add_headers(AccountKey = api_key)
)
if (httr::http_status(result)$category != "Success") {
message("Unsuccessful API call for VMS/EMAS messages. Please check your parameters or connection.")
return(result)
} else {
message("Successful API call for VMS/EMAS messages. Processing page ", num, "...")
}
output0 <- data.frame(matrix(nrow = 0, ncol = 12))
vms_list <- httr::content(result)[[2]]
for (i in 1:length(vms_list)) {
interim <- vms_list[[i]]
interim[sapply(interim, is.null)] <- 0
output0 <- rbind(output0, t(unlist(interim)))
}
output <- rbind(output, output0)
num <- num + 1
}
for (col in colnames(output)) {
output[[col]] <- as.character(output[[col]])
}
output$Latitude <- as.numeric(output$Latitude)
output$Longitude <- as.numeric(output$Longitude)
message("API call successful. Number of VMS/EMAS messages found: ", nrow(output))
return(output)
}
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