R/fars_functions.R

In csmollerlevet/trafficAccidents: Fatal injuries suffered in motor vehicle traffic crashes data

#' Reads a file and loads it into a tibble
#'
#' This is a simple function that loads the file indicated by filename into a ’tbl_df’ class (the ’tibble’)
#' that provides stricter checking and better formatting than the traditional data frame.
#'
#' @param filename A character string giving the name of the file to be loaded
#'
#' @return This function first checks if the file exists, if it doesn't it will return a message indicating that the file does not exist, if the file exists, it
#' returns the file contents formated into a tibble.
#'
#' @examples
#' fars_read('test.csv')
#' fars_read('test.txt')
#'
#' @export
#' @importFrom readr read_csv
fars_read <- function(filename) {
  if(!file.exists(filename))
    stop("file '", filename, "' does not exist")
  data <- suppressMessages({
    readr::read_csv(filename, progress = FALSE)
  })
  dplyr::tbl_df(data)
}
#'
#' Generates a file name based on the input year
#'
#' This is a simple function that produces the file name for the year requested
#'
#' @param year A character string giving the year of file name to be generated
#'
#' @return This function generates the file name (character string) corresponding to the year of interest. Available years are: 2013, 2014 and 2015.
#'
#' @examples
#' make_filename('2013')
#' make_filename('2014')
#'
#' @export
make_filename <- function(year) {
  year <- as.integer(year)
  sprintf("accident_%d.csv.bz2", year)
}
#'
#' Retrives MONTH and year column values for selected years
#'
#' For each year listed in the input, the function reads a file related to the year, checks if the year requested appears in the file column 'year', and if so, retrieves the month information for that year.
#' The output is a list of tibbles with two columns, one for MONTH and second for year.
#'
#' @param years A list of character strings giving the years of the files to be querried.
#'
#' @return This function returns the MONTH and year column values for the years (rows) indicated in the input list. If the year requested is invalid, it will return a message indicateing that the year is invalid.
#'
#' @examples
#' fars_read_years(list('2013','2014'))
#' fars_read_years(list('2013'))
#'
#' @export
#' @importFrom dplyr mutate select
fars_read_years <- function(years) {
  lapply(years, function(year) {
    file <- make_filename(year)
    tryCatch({
      dat <- fars_read(file)
      dplyr::mutate(dat, year = year) %>%
        dplyr::select(MONTH, year)
    }, error = function(e) {
      warning("invalid year: ", year)
      return(NULL)
    })
  })
}
#'
#' Summarises the number of accidents per month, per year.
#'
#' This function retrives MONTH and year column values for selected years and summarises the number of accidents per month, per year
#'
#' @param years A list of character strings giving the years of the files to be querried
#'
#' @return Retrives MONTH and year column values for selected years and summarises the number of accidents per month, per year, in a tibble with n+1 columns, were n is the number of years in the input list. The extra columns corresponds to the MONTH. Each cell corresponds to the number of accidents per month (rows), per year (columns).
#'
#' @examples
#' fars_summarize_years(list('2013','2014'))
#' fars_summarize_years(list('2013','2014','2015'))
#'
#' @export
#' @importFrom dplyr bind_rows group_by summarize
#' @importFrom tidyr spread
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)
}
#'
#' Plots accidents location per state, per year.
#'
#' This function plots a map of the selected state and marks the location of each accident during the selected year on the map.
#'
#' @param state.num An integer with values 1 to 56 corresponding to the 56 states of the united states
#' @param year A character strings indicating the year during which the accidents to be plotted occured
#'
#' @return A plot of the selected state with dots indicating the location of the accidents occured during the selected year. If there are no accidents to plot a message indicating that there are no accidents to report is printed.
#'
#' @examples
#' fars_map_state(state.num=1, year='2013')
#' fars_map_state(state.num=10, year='2014')
#'
#' @export
#' @importFrom dplyr filter
#' @importFrom maps map
#' @importFrom graphics points
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)
  })
}