In MahShaaban/fars:

knitr::opts_chunk$set(error = TRUE)

overview

This vignette is written for the package fars as part of week 4 assignment of the coursera course "R packages". The aim of this is to describe the functions in the package and their use cases. The packages consists of 5 functions:

• make_filename

• fars_read

• fars_read_years

• fars_summarize_year

• fars_map_state

Data

The functions provided for you in this assignment will be using data from the US National Highway Traffic Safety Administration's Fatality Analysis Reporting System, which is a nationwide census providing the American public yearly data regarding fatal injuries suffered in motor vehicle traffic crashes. Once the package is installed 3 example files are accessible as follows:

system.file('extdata', 'accident_2013.csv.bz2', package = 'fars')
system.file('extdata', 'accident_2014.csv.bz2', package = 'fars')
system.file('extdata', 'accident_2015.csv.bz2', package = 'fars')

I will use these files to explain the use of the functions in the package.

Functions

Using make_filenam

This function is used to construct a file name using the corresponding year. The following is an example to construct a FARS data file name for the year 2013.

library(fars)
library(maps)

make_filename(2013)

Using fars_read

This function is a wrapper of the readr::read_csv and customized to parse a FARS data file when exists otherwise returns an error. The following is an example of using the function to read the file that I constructed its name in the last example, then try read a file that doesn't exist.

# file exist
dat <- fars_read('accident_2013.csv.bz2')
class(dat)

# file does nott exist
fars_read('accident_1900.csv.bz2')

Using fars_read_years

This is a custom function that is used to parse a number of FARS data files for the corresponding input years. If first construct file names using make_filename then reads the files in a list using fars_read. The function returns a warning for years that do not exist, as in the following example.

# all years exist
yrs <- 2013:2015
dat <- fars_read_years(yrs)
class(dat)
identical(length(yrs), length(dat))

# year 2016 doesn't exist; warning returned
yrs <- 2013:2016
dat <- fars_read_years(yrs)

Using fars_summarize_years

This function provides a numerical summary of the total number of accidents per month for each year. It takes as input a years and wraps the previous functionality added to the summary. The following example uses the year 2013 as an input, the function will construct a file name and read the FARS data file then prints a summary.

yrs <- 2013:2015
fars_summarize_years(yrs)

Using fars_map_state

This function plots the coordinates of individual accidents for a particular year on a map of a particular state, state_num. An error is returned if the state.num is invalid and a message is returned when the number of accidents for this state is 0 at this year.

# valid input; plot returned
fars_map_state(50, 2013)

# invalid input; error returned
fars_map_state(500, 2013)

MahShaaban/fars documentation built on May 8, 2019, 3:21 p.m.