R

getwd()
list.files()

## Function provided is for the assignment US National Highway Traffic Safety Administration's Fatality Analysis Reporting System.

@details\Fatality Analysis Reporting System:
   \itemize{
   \item{url{https://www.nhtsa.gov/research-data/fatality-analysis-reporting-system-fars}}
   }

## Importing Libraries
@importFrom readr
@importFrom dplyr
@importFrom magrittr
@importFrom tidyr
@importFrom maps
@importFrom graphics

##Reading the fars_read
\code{fars_read}
@export
fars_read <- function(USNHT) {
  if(!file.exists(USNHT))
    stop("file '", USNHT, "' does not exist")
  data <- suppressMessages({
    readr::read_csv(USNHT, progress = FALSE)
  })
  dplyr::tbl_df(data)
}

##farsreadyears(year)
@export
farsreadyears <- function(years) {
  lapply(years, function(year) {
    file <- make_USNHT(year)
    tryCatch({
      dat <- fars_read(file)
      dplyr::mutate(dat, year = year) %>%
        dplyr::select(MONTH, year)
    }, error = function(e) {
      warning("invalid year: ", year)
      return(NULL)
    })
  })
}

## Summarizing FARS Data Via Years

@examples
plot(fars_summarize_years(2015))
fars_summarize_years(c(2015,2014))
@export
fars_summarize_years <- function(years) {
  dat_list <- fars_read_years(years)
  dplyr::bind_rows(dat_list) %>%
    dplyr::group_by(year, MONTH) %>%
    dplyr::summarize(n = n()) %>%
    tidyr::spread(year, n)
}


## fars_map_state

#' Error occurs when \code{state.num} is invalid
@examples
fars_map_state(38, 2015)
@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)
  })
}