knitr::opts_chunk$set(error = TRUE)
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
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.
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)
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')
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)
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)
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)
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