R/fars_map_state.R

In ekawabata/BuildingAnRPackage: Title: Useful functions for studying data from the US National Highway Traffic Safety Administration's Fatality Analysis Reporting System

#' Draws a map of accidents for a given state and year.
#'
#' @param state.num A numeric or character vector containing state number/s to plot
#' @param year A numeric containing which year to plot
#'
#' @return Returns a plot
#'
#' @importFrom dplyr filter
#' @importFrom graphics points
#' @importFrom maps map
#'
#' @note Produces an error if multiple years are given.  Produces an error if the state number does not exist but only a warning is given if multiple state numbers are given.
#'
#' @examples fars_map_state(1, 2013)
#'
#' @export
fars_map_state <- function(state.num, year) {
        filename <- make_filename(year)
        data <- fars_read(filename)
        state.num <- as.integer(state.num)

        if(!(state.num %in% unique(data$STATE)))
                stop("invalid STATE number: ", state.num)
        data.sub <- dplyr::filter(data, STATE == state.num)
        if(nrow(data.sub) == 0L) {
                message("no accidents to plot")
                return(invisible(NULL))
        }
        is.na(data.sub$LONGITUD) <- data.sub$LONGITUD > 900
        is.na(data.sub$LATITUDE) <- data.sub$LATITUDE > 90
        with(data.sub, {
                maps::map("state", ylim = range(LATITUDE, na.rm = TRUE),
                          xlim = range(LONGITUD, na.rm = TRUE))
                graphics::points(LONGITUD, LATITUDE, pch = 46)
        })
}