What we will cover today

• Just the tip of the iceberg...

• There's not enough time to cover everything

• The content presented today is largely based on the Data science in a Box materials

• Given our roles, we will focus on:

  1. How to start interacting with R

  2. How to wrangle data in R

Things we won't cover

...but I'll gladly help you with otherwise:

• Advanced data wrangling
• Detailed data visualization
• Data modelling
• Handling spatial data

Who Am I?

• Coordinator in Dr. Possemato's lab

• Fairly new to CIH (less than a year)

• Learned R (largely on my own) during graduate school

• Trained in biostats

• Enjoy the challenge of wrangling messy data

Toolkit

• Scriptability $\to$ R
• Literate programming (code, narrative, output in one place) $\to$ R Markdown
• Version control $\to$ Git / GitHub

Reproducibility checklist

Near-term goals:

• Are the tables and figures reproducible from the code and data?
• Does the code actually do what you think it does?
• In addition to what was done, is it clear why it was done? (e.g., how were parameter settings chosen?)

Long-term goals:

• Can the code be used for other data?
• Can you extend the code to do other things?

From manual tasking...

... to reproducible code

Reproducible plots

What is R

• R is a statistical programming language

• But why learn programming?

You must use a computer to do data science; you cannot do it in your head, or with pencil and paper.

Hadley Wickham

• Don't be discouraged by the word programming; R is first and foremost for data analysis

What is RStudio?

• RStudio is a convenient interface for R (an integreated development environment, IDE)
• At its simplest:^➥
  • R is like a car’s engine
  • RStudio is like a car’s dashboard

Let's take a tour - R / RStudio

Follow this link and log in with your google account:

https://rstudio.cloud/project/395951

Concepts introduced:

• Console
• Using R as a calculator
• Environment
• Loading and viewing a data frame
• Accessing a variable in a data frame
• R functions

R essentials

A short list (for now):

• Functions are (most often) verbs, followed by what they will be applied to in parantheses:

do_this(to_this)
do_that(to_this, to_that, with_those)

• Columns (variables) in data frames are accessed with $:

dataframe$var_name

• Packages are installed with the install.packages function and loaded with the library function, once per session:

install.packages("package_name")
library(package_name)

• For this project we'll need the following packages:

install.packages(c("tidyverse", "devtools", "datasauRus", "fivethirtyeight", "janitor", "DT"))

tidyverse

R Markdown

• Fully reproducible reports -- each time you knit the analysis is ran from the beginning

• Simple markdown syntax for text

• Code goes in chunks, defined by three backticks, narrative goes outside of chunks

Let's take a tour - R Markdown

Go to RStudio Cloud and open the application exercise Bechdel.

~/appex/ae-bechdel.Rmd

Concepts introduced:

• Knitting documents

• R Markdown and (some) R syntax

Bechdel Test

The Bechdel test asks whether a work of fiction features at least two women who talk to each other about something other than a man, and there must be two women named characters.

• Knit the R Markdown document.

Other things you can make in R Markdown

This presentation was written in R Markdown

HTML resume

Blog / Website

... ok, enough self promotion 👨‍💼

R Markdown help

R Markdown cheat sheet

Markdown Quick Reference
Help -> Markdown Quick Reference

Workspaces

Remember this, and expect it to bite you a few times as you're learning to work with R Markdown: The workspace of your R Markdown document is separate from the Console!

• Run the following in the console

x <- 2
x * 3

• Then, add the following chunk in your R Markdown document and knit it

x * 3

Version control

• GitHub as a platform for collaboration

• It's actually designed for version control

Versioning

Versioning

with human readable messages

Why do we need version control?

Git and GitHub tips

• Git is a version control system -- like “Track Changes” features from Microsoft Word on steroids. GitHub is the home for your Git-based projects on the internet -- like DropBox but much, much better).

• This is outside the scope of this workshop.

• There is a great resource for working with git and R: happygitwithr.com.

Tidy data

Happy families are all alike; every unhappy family is unhappy in its own way.

Leo Tolstoy

Summary tables

## # A tibble: 87 x 3
##    name               height  mass
##    <chr>               <int> <dbl>
##  1 Luke Skywalker        172    77
##  2 C-3PO                 167    75
##  3 R2-D2                  96    32
##  4 Darth Vader           202   136
##  5 Leia Organa           150    49
##  6 Owen Lars             178   120
##  7 Beru Whitesun lars    165    75
##  8 R5-D4                  97    32
##  9 Biggs Darklighter     183    84
## 10 Obi-Wan Kenobi        182    77
## # … with 77 more rows

## # A tibble: 5 x 2
##   gender        avg_height
##   <chr>              <dbl>
## 1 female              165.
## 2 hermaphrodite       175 
## 3 male                179.
## 4 none                200 
## 5 <NA>                120

Where does the name come from?

The pipe operator is implemented in the package magrittr, it's pronounced "and then".

Review: How does a pipe work?

• You can think about the following sequence of actions - find key, unlock car, start car, drive to school, park.

• Expressed as a set of nested functions in R pseudocode this would look like:

park(drive(start_car(find("keys")), to = "campus"))

• Writing it out using pipes give it a more natural (and easier to read) structure:

find("keys") %>%
  start_car() %>%
  drive(to = "campus") %>%
  park()

What about other arguments?

To send results to a function argument other than first one or to use the previous result for multiple arguments, use .:

starwars %>%
  filter(species == "Human") %>%
  lm(mass ~ height, data = .)

## 
## Call:
## lm(formula = mass ~ height, data = .)
## 
## Coefficients:
## (Intercept)       height  
##     -116.58         1.11

Bike crashes in NC 2007 - 2014

The dataset is in the dsbox package:

• github packages require special install commands

• the remotes package is automatically installed with devtools

remotes::install_github("rstudio-education/dsbox")
library(dsbox)
ncbikecrash

Variables

View the names of variables via

names(ncbikecrash)

##  [1] "object_id"            "city"                 "county"              
##  [4] "region"               "development"          "locality"            
##  [7] "on_road"              "rural_urban"          "speed_limit"         
## [10] "traffic_control"      "weather"              "workzone"            
## [13] "bike_age"             "bike_age_group"       "bike_alcohol"        
## [16] "bike_alcohol_drugs"   "bike_direction"       "bike_injury"         
## [19] "bike_position"        "bike_race"            "bike_sex"            
## [22] "driver_age"           "driver_age_group"     "driver_alcohol"      
## [25] "driver_alcohol_drugs" "driver_est_speed"     "driver_injury"       
## [28] "driver_race"          "driver_sex"           "driver_vehicle_type" 
## [31] "crash_alcohol"        "crash_date"           "crash_day"           
## [34] "crash_group"          "crash_hour"           "crash_location"      
## [37] "crash_month"          "crash_severity"       "crash_time"          
## [40] "crash_type"           "crash_year"           "ambulance_req"       
## [43] "hit_run"              "light_condition"      "road_character"      
## [46] "road_class"           "road_condition"       "road_configuration"  
## [49] "road_defects"         "road_feature"         "road_surface"        
## [52] "num_bikes_ai"         "num_bikes_bi"         "num_bikes_ci"        
## [55] "num_bikes_ki"         "num_bikes_no"         "num_bikes_to"        
## [58] "num_bikes_ui"         "num_lanes"            "num_units"           
## [61] "distance_mi_from"     "frm_road"             "rte_invd_cd"         
## [64] "towrd_road"           "geo_point"            "geo_shape"

and see detailed descriptions with ?ncbikecrash.

Viewing your data

• In the Environment, after loading with data(ncbikecrash), and click on the name of the data frame to view it in the data viewer

• Use the glimpse function to take a peek

glimpse(ncbikecrash)

## Observations: 7,467
## Variables: 66
## $ object_id            <int> 1686, 1674, 1673, 1687, 1653, 1665, 1642, 1…
## $ city                 <chr> "None - Rural Crash", "Henderson", "None - …
## $ county               <chr> "Wayne", "Vance", "Lincoln", "Columbus", "N…
## $ region               <chr> "Coastal", "Piedmont", "Piedmont", "Coastal…
## $ development          <chr> "Farms, Woods, Pastures", "Residential", "F…
## $ locality             <chr> "Rural (<30% Developed)", "Mixed (30% To 70…
## $ on_road              <chr> "SR 1915", "NICHOLAS ST", "US 321", "W BURK…
## $ rural_urban          <chr> "Rural", "Urban", "Rural", "Urban", "Urban"…
## $ speed_limit          <chr> "50 - 55  MPH", "30 - 35  MPH", "50 - 55  M…
## $ traffic_control      <chr> "No Control Present", "Stop Sign", "Double …
## $ weather              <chr> "Clear", "Clear", "Clear", "Rain", "Clear",…
## $ workzone             <chr> "No", "No", "No", "No", "No", "No", "No", "…
## $ bike_age             <chr> "52", "66", "33", "52", "22", "15", "41", "…
## $ bike_age_group       <chr> "50-59", "60-69", "30-39", "50-59", "20-24"…
## $ bike_alcohol         <chr> "No", "No", "No", "Yes", "No", "No", "No", …
## $ bike_alcohol_drugs   <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,…
## $ bike_direction       <chr> "With Traffic", "With Traffic", "With Traff…
## $ bike_injury          <chr> "B: Evident Injury", "C: Possible Injury", …
## $ bike_position        <chr> "Bike Lane / Paved Shoulder", "Travel Lane"…
## $ bike_race            <chr> "Black", "Black", "White", "Black", "White"…
## $ bike_sex             <chr> "Male", "Male", "Male", "Male", "Female", "…
## $ driver_age           <chr> "34", NA, "37", "55", "25", "17", NA, "50",…
## $ driver_age_group     <chr> "30-39", NA, "30-39", "50-59", "25-29", "0-…
## $ driver_alcohol       <chr> "No", "Missing", "No", "No", "No", "No", "M…
## $ driver_alcohol_drugs <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,…
## $ driver_est_speed     <chr> "51-55 mph", "6-10 mph", "41-45 mph", "11-1…
## $ driver_injury        <chr> "O: No Injury", "Unknown Injury", "O: No In…
## $ driver_race          <chr> "White", "Unknown/Missing", "Hispanic", "Bl…
## $ driver_sex           <chr> "Male", NA, "Female", "Male", "Male", "Fema…
## $ driver_vehicle_type  <chr> "Single Unit Truck (2-Axle, 6-Tire)", NA, "…
## $ crash_alcohol        <chr> "No", "No", "No", "Yes", "No", "No", "No", …
## $ crash_date           <chr> "11DEC2013", "20NOV2013", "03NOV2013", "14D…
## $ crash_day            <chr> "Wednesday", "Wednesday", "Sunday", "Saturd…
## $ crash_group          <chr> "Motorist Overtaking Bicyclist", "Bicyclist…
## $ crash_hour           <int> 6, 20, 18, 18, 13, 17, 17, 7, 15, 2, 12, 22…
## $ crash_location       <chr> "Non-Intersection", "Intersection", "Non-In…
## $ crash_month          <chr> "December", "November", "November", "Decemb…
## $ crash_severity       <chr> "B: Evident Injury", "C: Possible Injury", …
## $ crash_time           <drtn> 06:10:00, 20:41:00, 18:05:00, 18:34:00, 13…
## $ crash_type           <chr> "Motorist Overtaking - Undetected Bicyclist…
## $ crash_year           <int> 2013, 2013, 2013, 2013, 2013, 2013, 2013, 2…
## $ ambulance_req        <chr> "Yes", "No", "Yes", "Yes", "Yes", "Yes", "Y…
## $ hit_run              <chr> "No", "Yes", "No", "No", "No", "No", "Yes",…
## $ light_condition      <chr> "Dark - Roadway Not Lighted", NA, "Dark - R…
## $ road_character       <chr> "Straight - Level", "Straight - Level", "St…
## $ road_class           <chr> "State Secondary Route", "Local Street", "U…
## $ road_condition       <chr> "Dry", "Dry", "Dry", "Water (Standing, Movi…
## $ road_configuration   <chr> "Two-Way, Not Divided", "Two-Way, Divided, …
## $ road_defects         <chr> "None", NA, "None", "None", "None", "None",…
## $ road_feature         <chr> "No Special Feature", "T-Intersection", "No…
## $ road_surface         <chr> "Coarse Asphalt", "Smooth Asphalt", "Smooth…
## $ num_bikes_ai         <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ num_bikes_bi         <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ num_bikes_ci         <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ num_bikes_ki         <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ num_bikes_no         <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ num_bikes_to         <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ num_bikes_ui         <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ num_lanes            <chr> "2 lanes", "2 lanes", "2 lanes", "1 lane", …
## $ num_units            <int> 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2…
## $ distance_mi_from     <chr> "0", "0", "0", "0", "0", "0", "0", "0", "0"…
## $ frm_road             <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,…
## $ rte_invd_cd          <int> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ towrd_road           <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,…
## $ geo_point            <chr> "35.3336070056, -77.9955023901", "36.315187…
## $ geo_shape            <chr> "{\"type\": \"Point\", \"coordinates\": [-7…

A Grammar of Data Manipulation

dplyr is based on the concepts of functions as verbs that manipulate data frames.

dplyr rules for functions

• First argument is always a data frame

• Subsequent arguments say what to do with that data frame

• Always return a data frame

• Don't modify in place

A note on piping and layering

• The %>% operator in dplyr functions is called the pipe operator. This means you "pipe" the output of the previous line of code as the first input of the next line of code.

• The + operator in ggplot2 functions is used for "layering". This means you create the plot in layers, separated by +.

filter to select a subset of rows

for crashes in Durham County

ncbikecrash %>%
  filter(county == "Durham")

## # A tibble: 340 x 66
##    object_id city  county region development locality on_road rural_urban
##        <int> <chr> <chr>  <chr>  <chr>       <chr>    <chr>   <chr>      
##  1      2452 Durh… Durham Piedm… Residential Urban (… <NA>    Urban      
##  2      2441 Durh… Durham Piedm… Commercial  Urban (… <NA>    Urban      
##  3      2466 Durh… Durham Piedm… Commercial  Urban (… <NA>    Urban      
##  4       549 Durh… Durham Piedm… Residential Urban (… PARK A… Urban      
##  5       598 Durh… Durham Piedm… Residential Urban (… BELT S… Urban      
##  6       603 Durh… Durham Piedm… Residential Urban (… HINSON… Urban      
##  7      3974 Durh… Durham Piedm… Commercial  Urban (… <NA>    Urban      
##  8      7134 Durh… Durham Piedm… Commercial  Urban (… <NA>    Urban      
##  9      1670 Durh… Durham Piedm… Commercial  Urban (… INFINI… Urban      
## 10      1773 Durh… Durham Piedm… Residential Urban (… <NA>    Urban      
## # … with 330 more rows, and 58 more variables: speed_limit <chr>,
## #   traffic_control <chr>, weather <chr>, workzone <chr>, bike_age <chr>,
## #   bike_age_group <chr>, bike_alcohol <chr>, bike_alcohol_drugs <chr>,
## #   bike_direction <chr>, bike_injury <chr>, bike_position <chr>,
## #   bike_race <chr>, bike_sex <chr>, driver_age <chr>,
## #   driver_age_group <chr>, driver_alcohol <chr>,
## #   driver_alcohol_drugs <chr>, driver_est_speed <chr>,
## #   driver_injury <chr>, driver_race <chr>, driver_sex <chr>,
## #   driver_vehicle_type <chr>, crash_alcohol <chr>, crash_date <chr>,
## #   crash_day <chr>, crash_group <chr>, crash_hour <int>,
## #   crash_location <chr>, crash_month <chr>, crash_severity <chr>,
## #   crash_time <drtn>, crash_type <chr>, crash_year <int>,
## #   ambulance_req <chr>, hit_run <chr>, light_condition <chr>,
## #   road_character <chr>, road_class <chr>, road_condition <chr>,
## #   road_configuration <chr>, road_defects <chr>, road_feature <chr>,
## #   road_surface <chr>, num_bikes_ai <int>, num_bikes_bi <int>,
## #   num_bikes_ci <int>, num_bikes_ki <int>, num_bikes_no <int>,
## #   num_bikes_to <int>, num_bikes_ui <int>, num_lanes <chr>,
## #   num_units <int>, distance_mi_from <chr>, frm_road <chr>,
## #   rte_invd_cd <int>, towrd_road <chr>, geo_point <chr>, geo_shape <chr>

filter for many conditions at once

for crashes in Durham County where biker was 0-5 years old

ncbikecrash %>%
  filter(county == "Durham", bike_age_group == "0-5")

## # A tibble: 4 x 66
##   object_id city  county region development locality on_road rural_urban
##       <int> <chr> <chr>  <chr>  <chr>       <chr>    <chr>   <chr>      
## 1      4062 Durh… Durham Piedm… Residential Urban (… <NA>    Urban      
## 2       414 Durh… Durham Piedm… Residential Urban (… PVA 90… Urban      
## 3      3016 Durh… Durham Piedm… Residential Urban (… <NA>    Urban      
## 4      1383 Durh… Durham Piedm… Residential Urban (… PVA 62… Urban      
## # … with 58 more variables: speed_limit <chr>, traffic_control <chr>,
## #   weather <chr>, workzone <chr>, bike_age <chr>, bike_age_group <chr>,
## #   bike_alcohol <chr>, bike_alcohol_drugs <chr>, bike_direction <chr>,
## #   bike_injury <chr>, bike_position <chr>, bike_race <chr>,
## #   bike_sex <chr>, driver_age <chr>, driver_age_group <chr>,
## #   driver_alcohol <chr>, driver_alcohol_drugs <chr>,
## #   driver_est_speed <chr>, driver_injury <chr>, driver_race <chr>,
## #   driver_sex <chr>, driver_vehicle_type <chr>, crash_alcohol <chr>,
## #   crash_date <chr>, crash_day <chr>, crash_group <chr>,
## #   crash_hour <int>, crash_location <chr>, crash_month <chr>,
## #   crash_severity <chr>, crash_time <drtn>, crash_type <chr>,
## #   crash_year <int>, ambulance_req <chr>, hit_run <chr>,
## #   light_condition <chr>, road_character <chr>, road_class <chr>,
## #   road_condition <chr>, road_configuration <chr>, road_defects <chr>,
## #   road_feature <chr>, road_surface <chr>, num_bikes_ai <int>,
## #   num_bikes_bi <int>, num_bikes_ci <int>, num_bikes_ki <int>,
## #   num_bikes_no <int>, num_bikes_to <int>, num_bikes_ui <int>,
## #   num_lanes <chr>, num_units <int>, distance_mi_from <chr>,
## #   frm_road <chr>, rte_invd_cd <int>, towrd_road <chr>, geo_point <chr>,
## #   geo_shape <chr>

Logical operators in R

select to keep variables

ncbikecrash %>%
  filter(county == "Durham", bike_age_group == "0-5") %>%
  select(locality, speed_limit)

## # A tibble: 4 x 2
##   locality               speed_limit 
##   <chr>                  <chr>       
## 1 Urban (>70% Developed) 30 - 35  MPH
## 2 Urban (>70% Developed) 5 - 15 MPH  
## 3 Urban (>70% Developed) 20 - 25  MPH
## 4 Urban (>70% Developed) 20 - 25  MPH

select to exclude variables

ncbikecrash %>%
  select(-object_id)

## # A tibble: 7,467 x 65
##    city  county region development locality on_road rural_urban speed_limit
##    <chr> <chr>  <chr>  <chr>       <chr>    <chr>   <chr>       <chr>      
##  1 None… Wayne  Coast… Farms, Woo… Rural (… SR 1915 Rural       50 - 55  M…
##  2 Hend… Vance  Piedm… Residential Mixed (… NICHOL… Urban       30 - 35  M…
##  3 None… Linco… Piedm… Farms, Woo… Rural (… US 321  Rural       50 - 55  M…
##  4 Whit… Colum… Coast… Commercial  Urban (… W BURK… Urban       30 - 35  M…
##  5 Wilm… New H… Coast… Residential Urban (… RACINE… Urban       <NA>       
##  6 None… Robes… Coast… Farms, Woo… Rural (… SR 1513 Rural       50 - 55  M…
##  7 None… Richm… Piedm… Residential Mixed (… SR 1903 Rural       30 - 35  M…
##  8 Rale… Wake   Piedm… Commercial  Urban (… PERSON… Urban       30 - 35  M…
##  9 Whit… Colum… Coast… Residential Rural (… FLOWER… Urban       30 - 35  M…
## 10 New … Craven Coast… Residential Urban (… SUTTON… Urban       20 - 25  M…
## # … with 7,457 more rows, and 57 more variables: traffic_control <chr>,
## #   weather <chr>, workzone <chr>, bike_age <chr>, bike_age_group <chr>,
## #   bike_alcohol <chr>, bike_alcohol_drugs <chr>, bike_direction <chr>,
## #   bike_injury <chr>, bike_position <chr>, bike_race <chr>,
## #   bike_sex <chr>, driver_age <chr>, driver_age_group <chr>,
## #   driver_alcohol <chr>, driver_alcohol_drugs <chr>,
## #   driver_est_speed <chr>, driver_injury <chr>, driver_race <chr>,
## #   driver_sex <chr>, driver_vehicle_type <chr>, crash_alcohol <chr>,
## #   crash_date <chr>, crash_day <chr>, crash_group <chr>,
## #   crash_hour <int>, crash_location <chr>, crash_month <chr>,
## #   crash_severity <chr>, crash_time <drtn>, crash_type <chr>,
## #   crash_year <int>, ambulance_req <chr>, hit_run <chr>,
## #   light_condition <chr>, road_character <chr>, road_class <chr>,
## #   road_condition <chr>, road_configuration <chr>, road_defects <chr>,
## #   road_feature <chr>, road_surface <chr>, num_bikes_ai <int>,
## #   num_bikes_bi <int>, num_bikes_ci <int>, num_bikes_ki <int>,
## #   num_bikes_no <int>, num_bikes_to <int>, num_bikes_ui <int>,
## #   num_lanes <chr>, num_units <int>, distance_mi_from <chr>,
## #   frm_road <chr>, rte_invd_cd <int>, towrd_road <chr>, geo_point <chr>,
## #   geo_shape <chr>

select a range of variables

ncbikecrash %>%
  select(city:locality)

## # A tibble: 7,467 x 5
##    city           county     region  development       locality            
##    <chr>          <chr>      <chr>   <chr>             <chr>               
##  1 None - Rural … Wayne      Coastal Farms, Woods, Pa… Rural (<30% Develop…
##  2 Henderson      Vance      Piedmo… Residential       Mixed (30% To 70% D…
##  3 None - Rural … Lincoln    Piedmo… Farms, Woods, Pa… Rural (<30% Develop…
##  4 Whiteville     Columbus   Coastal Commercial        Urban (>70% Develop…
##  5 Wilmington     New Hanov… Coastal Residential       Urban (>70% Develop…
##  6 None - Rural … Robeson    Coastal Farms, Woods, Pa… Rural (<30% Develop…
##  7 None - Rural … Richmond   Piedmo… Residential       Mixed (30% To 70% D…
##  8 Raleigh        Wake       Piedmo… Commercial        Urban (>70% Develop…
##  9 Whiteville     Columbus   Coastal Residential       Rural (<30% Develop…
## 10 New Bern       Craven     Coastal Residential       Urban (>70% Develop…
## # … with 7,457 more rows

slice for certain row numbers

First five

ncbikecrash %>%
  slice(1:5)

## # A tibble: 5 x 66
##   object_id city  county region development locality on_road rural_urban
##       <int> <chr> <chr>  <chr>  <chr>       <chr>    <chr>   <chr>      
## 1      1686 None… Wayne  Coast… Farms, Woo… Rural (… SR 1915 Rural      
## 2      1674 Hend… Vance  Piedm… Residential Mixed (… NICHOL… Urban      
## 3      1673 None… Linco… Piedm… Farms, Woo… Rural (… US 321  Rural      
## 4      1687 Whit… Colum… Coast… Commercial  Urban (… W BURK… Urban      
## 5      1653 Wilm… New H… Coast… Residential Urban (… RACINE… Urban      
## # … with 58 more variables: speed_limit <chr>, traffic_control <chr>,
## #   weather <chr>, workzone <chr>, bike_age <chr>, bike_age_group <chr>,
## #   bike_alcohol <chr>, bike_alcohol_drugs <chr>, bike_direction <chr>,
## #   bike_injury <chr>, bike_position <chr>, bike_race <chr>,
## #   bike_sex <chr>, driver_age <chr>, driver_age_group <chr>,
## #   driver_alcohol <chr>, driver_alcohol_drugs <chr>,
## #   driver_est_speed <chr>, driver_injury <chr>, driver_race <chr>,
## #   driver_sex <chr>, driver_vehicle_type <chr>, crash_alcohol <chr>,
## #   crash_date <chr>, crash_day <chr>, crash_group <chr>,
## #   crash_hour <int>, crash_location <chr>, crash_month <chr>,
## #   crash_severity <chr>, crash_time <drtn>, crash_type <chr>,
## #   crash_year <int>, ambulance_req <chr>, hit_run <chr>,
## #   light_condition <chr>, road_character <chr>, road_class <chr>,
## #   road_condition <chr>, road_configuration <chr>, road_defects <chr>,
## #   road_feature <chr>, road_surface <chr>, num_bikes_ai <int>,
## #   num_bikes_bi <int>, num_bikes_ci <int>, num_bikes_ki <int>,
## #   num_bikes_no <int>, num_bikes_to <int>, num_bikes_ui <int>,
## #   num_lanes <chr>, num_units <int>, distance_mi_from <chr>,
## #   frm_road <chr>, rte_invd_cd <int>, towrd_road <chr>, geo_point <chr>,
## #   geo_shape <chr>

slice for certain row numbers

Last five

last_row <- nrow(ncbikecrash)
ncbikecrash %>%
  slice((last_row - 4):last_row)

## # A tibble: 5 x 66
##   object_id city  county region development locality on_road rural_urban
##       <int> <chr> <chr>  <chr>  <chr>       <chr>    <chr>   <chr>      
## 1      6989 High… Guilf… Piedm… Residential Urban (… <NA>    Urban      
## 2      6991 Wilm… New H… Coast… Residential Urban (… <NA>    Urban      
## 3      6995 Kins… Lenoir Coast… Commercial  Urban (… <NA>    Urban      
## 4      6998 Faye… Cumbe… Coast… Residential Urban (… <NA>    Urban      
## 5      7000 None… Onslow Coast… Farms, Woo… Rural (… <NA>    Rural      
## # … with 58 more variables: speed_limit <chr>, traffic_control <chr>,
## #   weather <chr>, workzone <chr>, bike_age <chr>, bike_age_group <chr>,
## #   bike_alcohol <chr>, bike_alcohol_drugs <chr>, bike_direction <chr>,
## #   bike_injury <chr>, bike_position <chr>, bike_race <chr>,
## #   bike_sex <chr>, driver_age <chr>, driver_age_group <chr>,
## #   driver_alcohol <chr>, driver_alcohol_drugs <chr>,
## #   driver_est_speed <chr>, driver_injury <chr>, driver_race <chr>,
## #   driver_sex <chr>, driver_vehicle_type <chr>, crash_alcohol <chr>,
## #   crash_date <chr>, crash_day <chr>, crash_group <chr>,
## #   crash_hour <int>, crash_location <chr>, crash_month <chr>,
## #   crash_severity <chr>, crash_time <drtn>, crash_type <chr>,
## #   crash_year <int>, ambulance_req <chr>, hit_run <chr>,
## #   light_condition <chr>, road_character <chr>, road_class <chr>,
## #   road_condition <chr>, road_configuration <chr>, road_defects <chr>,
## #   road_feature <chr>, road_surface <chr>, num_bikes_ai <int>,
## #   num_bikes_bi <int>, num_bikes_ci <int>, num_bikes_ki <int>,
## #   num_bikes_no <int>, num_bikes_to <int>, num_bikes_ui <int>,
## #   num_lanes <chr>, num_units <int>, distance_mi_from <chr>,
## #   frm_road <chr>, rte_invd_cd <int>, towrd_road <chr>, geo_point <chr>,
## #   geo_shape <chr>

pull to extract a column as a vector

ncbikecrash %>%
  slice(1:6) %>%
  pull(locality)

## [1] "Rural (<30% Developed)"       "Mixed (30% To 70% Developed)"
## [3] "Rural (<30% Developed)"       "Urban (>70% Developed)"      
## [5] "Urban (>70% Developed)"       "Rural (<30% Developed)"

vs.

ncbikecrash %>%
  slice(1:6) %>%
  select(locality)

## # A tibble: 6 x 1
##   locality                    
##   <chr>                       
## 1 Rural (<30% Developed)      
## 2 Mixed (30% To 70% Developed)
## 3 Rural (<30% Developed)      
## 4 Urban (>70% Developed)      
## 5 Urban (>70% Developed)      
## 6 Rural (<30% Developed)

sample_n / sample_frac for a random sample

• sample_n: randomly sample 5 observations

ncbikecrash_n5 <- ncbikecrash %>%
  sample_n(5, replace = FALSE)
dim(ncbikecrash_n5)

## [1]  5 66

• sample_frac: randomly sample 20% of observations

ncbikecrash_perc20 <-ncbikecrash %>%
  sample_frac(0.2, replace = FALSE)
dim(ncbikecrash_perc20)

## [1] 1493   66

distinct to filter for unique rows

And arrange to order alphabetically

ncbikecrash %>% 
  select(county, city) %>% 
  distinct() %>% 
  arrange(county, city)

## # A tibble: 391 x 2
##    county    city              
##    <chr>     <chr>             
##  1 Alamance  Alamance          
##  2 Alamance  Burlington        
##  3 Alamance  Elon              
##  4 Alamance  Elon College      
##  5 Alamance  Gibsonville       
##  6 Alamance  Graham            
##  7 Alamance  Green Level       
##  8 Alamance  Mebane            
##  9 Alamance  None - Rural Crash
## 10 Alexander None - Rural Crash
## # … with 381 more rows

summarise to reduce variables to values

ncbikecrash %>%
  summarise(avg_hr = mean(crash_hour))

## # A tibble: 1 x 1
##   avg_hr
##    <dbl>
## 1   14.7

group_by to do calculations on groups

ncbikecrash %>%
  group_by(hit_run) %>%
  summarise(avg_hr = mean(crash_hour))

## # A tibble: 2 x 2
##   hit_run avg_hr
##   <chr>    <dbl>
## 1 No        14.6
## 2 Yes       15.0

count observations in groups

ncbikecrash %>%
  count(driver_alcohol_drugs)

## # A tibble: 6 x 2
##   driver_alcohol_drugs                    n
##   <chr>                               <int>
## 1 Missing                                99
## 2 No                                    695
## 3 Yes-Alcohol,  impairment suspected     12
## 4 Yes-Alcohol, no impairment detected     3
## 5 Yes-Drugs, impairment suspected         4
## 6 <NA>                                 6654

mutate to add new variables

ncbikecrash %>%
  mutate(driver_alcohol_drugs_simplified = case_when(
    driver_alcohol_drugs == "Missing"       ~ NA,
    str_detect(driver_alcohol_drugs, "Yes") ~ "Yes",
    TRUE                                    ~ "No"
  ))

"Save" when you mutate

Most often when you define a new variable with mutate you'll also want to save the resulting data frame, often by writing over the original data frame.

ncbikecrash <- ncbikecrash %>%
  mutate(driver_alcohol_drugs_simplified = case_when(
    str_detect(driver_alcohol_drugs, "Yes") ~ "Yes",
    TRUE                                    ~ driver_alcohol_drugs
  ))

Check before you move on

ncbikecrash %>% 
  count(driver_alcohol_drugs, driver_alcohol_drugs_simplified)

## # A tibble: 6 x 3
##   driver_alcohol_drugs                driver_alcohol_drugs_simplified     n
##   <chr>                               <chr>                           <int>
## 1 Missing                             Missing                            99
## 2 No                                  No                                695
## 3 Yes-Alcohol,  impairment suspected  Yes                                12
## 4 Yes-Alcohol, no impairment detected Yes                                 3
## 5 Yes-Drugs, impairment suspected     Yes                                 4
## 6 <NA>                                <NA>                             6654

ncbikecrash %>% 
  count(driver_alcohol_drugs_simplified)

## # A tibble: 4 x 2
##   driver_alcohol_drugs_simplified     n
##   <chr>                           <int>
## 1 Missing                            99
## 2 No                                695
## 3 Yes                                19
## 4 <NA>                             6654

AE - NC bike crashes

• Go to the cloud project and open application exercise NC bike crashes

  ~appex/ae-ncbikecrashes.Rmd

• For each question you work on, set the eval chunk option to TRUE and knit

Style guide

Good coding style is like correct punctuation: you can manage without it, butitsuremakesthingseasiertoread.

Hadley Wickham

• Style guide for this course is based on the Tidyverse style guide: http://style.tidyverse.org/

• There's more to it than what we'll cover today, but we'll mention more as we introduce more functionality, and do a recap later in the semester

File names and code chunk labels

• Do not use spaces in file names, use - or _ to separate words
• Use all lowercase letters

# Good
ucb-admit.csv
# Bad
UCB Admit.csv

Object names

• Use _ to separate words in object names
• Use informative but short object names
• Do not reuse object names within an analysis

# Good
acs_employed
# Bad
acs.employed
acs2
acs_subset
acs_subsetted_for_males

Spacing

• Put a space before and after all infix operators (=, +, -, <-, etc.), and when naming arguments in function calls.
• Always put a space after a comma, and never before (just like in regular English).

# Good
average <- mean(feet / 12 + inches, na.rm = TRUE)
# Bad
average<-mean(feet/12+inches,na.rm=TRUE)

ggplot

• Always end a line with +
• Always indent the next line

# Good
ggplot(diamonds, mapping = aes(x = price)) +
  geom_histogram()
# Bad
ggplot(diamonds,mapping=aes(x=price))+geom_histogram()

Long lines

• Limit your code to 80 characters per line. This fits comfortably on a printed page with a reasonably sized font.
• Take advantage of RStudio editor's auto formatting for indentation at line breaks.

Assignment

• Use <- not =

# Good
x <- 2
# Bad
x = 2

Quotes

Use ", not ', for quoting text. The only exception is when the text already contains double quotes and no single quotes.

ggplot(diamonds, mapping = aes(x = price)) +
  geom_histogram() +
  # Good
  labs(title = "`Shine bright like a diamond`",
  # Good
       x = "Diamond prices",
  # Bad
       y = 'Frequency')

Data types in R

• logical
• double
• integer
• character
• lists
• and some more, but we won't be focusing on those

Logical & character

logical - boolean values TRUE and FALSE

typeof(TRUE)

## [1] "logical"

character - character strings

typeof("hello")

## [1] "character"

typeof('world') # but remember, we use double quotations!

## [1] "character"

Double & integer

double - floating point numerical values (default numerical type)

typeof(1.335)

## [1] "double"

typeof(7)

## [1] "double"

integer - integer numerical values (indicated with an L)

typeof(7L)

## [1] "integer"

typeof(1:3)

## [1] "integer"

Lists

Lists are 1d objects that can contain any combination of R objects

mylist <- list("A", 1:4, c(TRUE, FALSE), (1:4)/2)
mylist

## [[1]]
## [1] "A"
## 
## [[2]]
## [1] 1 2 3 4
## 
## [[3]]
## [1]  TRUE FALSE
## 
## [[4]]
## [1] 0.5 1.0 1.5 2.0

str(mylist)

## List of 4
##  $ : chr "A"
##  $ : int [1:4] 1 2 3 4
##  $ : logi [1:2] TRUE FALSE
##  $ : num [1:4] 0.5 1 1.5 2

Named lists

Because of their more complex structure we often want to name the elements of a list (we can also do this with vectors). This can make reading and accessing the list more straight forward.

myotherlist <- list(A = "hello", B = 1:4, "knock knock" = "who's there?")
str(myotherlist)

## List of 3
##  $ A          : chr "hello"
##  $ B          : int [1:4] 1 2 3 4
##  $ knock knock: chr "who's there?"

names(myotherlist)

## [1] "A"           "B"           "knock knock"

myotherlist$B

## [1] 1 2 3 4

Concatenation

Vectors can be constructed using the c() function.

c(1, 2, 3)

## [1] 1 2 3

c("Hello", "World!")

## [1] "Hello"  "World!"

c(1, c(2, c(3)))

## [1] 1 2 3

Coercion

R is a dynamically typed language -- it will happily convert between the various types without complaint.

c(1, "Hello")

## [1] "1"     "Hello"

c(FALSE, 3L)

## [1] 0 3

c(1.2, 3L)

## [1] 1.2 3.0

Missing Values

R uses NA to represent missing values in its data structures.

typeof(NA)

## [1] "logical"

Other Special Values

NaN - Not a number

Inf - Positive infinity

-Inf - Negative infinity

pi / 0

## [1] Inf

0 / 0

## [1] NaN

1/0 + 1/0

## [1] Inf

1/0 - 1/0

## [1] NaN

NaN / NA

## [1] NaN

NaN * NA

## [1] NaN

Activity

• c(1, NA+1L, "C")
• c(1L / 0, NA)
• c(1:3, 5)
• c(3L, NaN+1L)
• c(NA, TRUE)

Example: Cat lovers

Go to RStudio Cloud and open the application exercise Cat Lovers.

~/appex/ae-catlovers.Rmd

A survey asked respondents their name and number of cats. The instructions said to enter the number of cats as a numerical value.

cat_lovers <- read_csv("../data/cat-lovers.csv")

Oh why won't you work?!

cat_lovers %>%
  summarise(mean = mean(number_of_cats))

## # A tibble: 1 x 1
##    mean
##   <dbl>
## 1    NA

Oh why won't you still work??!!

cat_lovers %>%
  summarise(mean_cats = mean(number_of_cats, na.rm = TRUE))

## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1        NA

Take a breath and look at your data

glimpse(cat_lovers)

## Observations: 60
## Variables: 3
## $ name           <chr> "Bernice Warren", "Woodrow Stone", "Willie Bass",…
## $ number_of_cats <chr> "0", "0", "1", "3", "3", "2", "1", "1", "0", "0",…
## $ handedness     <chr> "left", "left", "left", "left", "left", "left", "…

Let's take another look

Sometimes you need to babysit your respondents

cat_lovers %>%
  mutate(number_of_cats = case_when(
    name == "Ginger Clark" ~ 2,
    name == "Doug Bass"    ~ 3,
    TRUE                   ~ as.numeric(number_of_cats)
    )) %>%
  summarise(mean_cats = mean(number_of_cats))

## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1     0.817

Always you need to respect data types

cat_lovers %>%
  mutate(
    number_of_cats = case_when(
      name == "Ginger Clark" ~ "2",
      name == "Doug Bass"    ~ "3",
      TRUE                   ~ number_of_cats
      ),
    number_of_cats = as.numeric(number_of_cats)
    ) %>%
  summarise(mean_cats = mean(number_of_cats))

## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1     0.817

Now that we know what we're doing...

cat_lovers <- cat_lovers %>%
  mutate(
    number_of_cats = case_when(
      name == "Ginger Clark" ~ "2",
      name == "Doug Bass"    ~ "3",
      TRUE                   ~ number_of_cats
      ),
    number_of_cats = as.numeric(number_of_cats)
    )

Moral of the story

• If your data does not behave how you expect it to, type coercion upon reading in the data might be the reason.

• Go in and investigate your data, apply the fix, save your data, live happily ever after.

Vectors vs. lists

x <- c(8,4,7)

x[1]

## [1] 8

x[[1]]

## [1] 8

y <- list(8,4,7)

y[2]

## [[1]]
## [1] 4

y[[2]]

## [1] 4

Note: When using tidyverse code you'll rarely need to refer to elements using square brackets, but it's good to be aware of this syntax, especially since you might encounter it when searching for help online.

Data "sets" in R

• "set" is in quotation marks because it is not a formal data class

• A tidy data "set" can be one of the following types:

  • tibble
  • data.frame

• We'll often work with tibbles:

  • readr package (e.g. read_csv function) loads data as a tibble by default
  • tibbles are part of the tidyverse, so they work well with other packages we are using
  • they make minimal assumptions about your data, so are less likely to cause hard to track bugs in your code

Data frames

• A data frame is the most commonly used data structure in R, they are just a list of equal length vectors (usually atomic, but you can use generic as well). Each vector is treated as a column and elements of the vectors as rows.

• A tibble is a type of data frame that ... makes your life (i.e. data analysis) easier.

• Most often a data frame will be constructed by reading in from a file, but we can also create them from scratch.

df <- tibble(x = 1:3, y = c("a", "b", "c"))
class(df)

## [1] "tbl_df"     "tbl"        "data.frame"

glimpse(df)

## Observations: 3
## Variables: 2
## $ x <int> 1, 2, 3
## $ y <chr> "a", "b", "c"

Data frames (cont.)

attributes(df)

## $names
## [1] "x" "y"
## 
## $row.names
## [1] 1 2 3
## 
## $class
## [1] "tbl_df"     "tbl"        "data.frame"

class(df$x)

## [1] "integer"

class(df$y)

## [1] "character"

Working with tibbles in pipelines

mean_cats <- cat_lovers %>%
  summarise(mean_cats = mean(number_of_cats))
cat_lovers %>%
  filter(number_of_cats < mean_cats) %>%
  nrow()

## [1] 60

A result of a pipeline is always a tibble

mean_cats

## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1     0.817

class(mean_cats)

## [1] "tbl_df"     "tbl"        "data.frame"

pull() can be your new best friend

But use it sparingly!

mean_cats <- cat_lovers %>%
  summarise(mean_cats = mean(number_of_cats)) %>%
  pull()
cat_lovers %>%
  filter(number_of_cats < mean_cats) %>%
  nrow()

## [1] 33

mean_cats

## [1] 0.8166667

class(mean_cats)

## [1] "numeric"

Factors

Factor objects are how R stores data for categorical variables (fixed numbers of discrete values).

(x = factor(c("BS", "MS", "PhD", "MS")))

## [1] BS  MS  PhD MS 
## Levels: BS MS PhD

glimpse(x)

##  Factor w/ 3 levels "BS","MS","PhD": 1 2 3 2

typeof(x)

## [1] "integer"

Read data in as character strings

glimpse(cat_lovers)

## Observations: 60
## Variables: 3
## $ name           <chr> "Bernice Warren", "Woodrow Stone", "Willie Bass",…
## $ number_of_cats <dbl> 0, 0, 1, 3, 3, 2, 1, 1, 0, 0, 0, 0, 1, 3, 3, 2, 1…
## $ handedness     <chr> "left", "left", "left", "left", "left", "left", "…

But coerce when plotting

p <- ggplot(cat_lovers, mapping = aes(x = handedness)) +
  geom_bar()
p

Use forcats to manipulate factors

cat_lovers <- cat_lovers %>%
  mutate(handedness = fct_relevel(handedness, 
                                  "right", "left", "ambidextrous"))

p <- ggplot(cat_lovers, mapping = aes(x = handedness)) +
  geom_bar()
p

Come for the functionality

• R uses factors to handle categorical variables, variables that have a fixed and known set of possible values. Historically, factors were much easier to work with than character vectors, so many base R functions automatically convert character vectors to factors.

• However, factors are still useful when you have true categorical data, and when you want to override the ordering of character vectors to improve display. The goal of the forcats package is to provide a suite of useful tools that solve common problems with factors.

Recap

• Always best to think of data as part of a tibble

  • This plays nicely with the tidyverse as well
  • Rows are observations, columns are variables

• Be careful about data types / classes

  • Sometimes R makes silly assumptions about your data class
    • Using tibbles help, but it might not solve all issues
    • Think about your data in context, e.g. 0/1 variable is most likely a factor
  • If a plot/output is not behaving the way you expect, first investigate the data class
  • If you are absolutely sure of a data class, overwrite it in your tibble so that you don't need to keep having to keep track of it
    • mutate the variable with the correct class

• Check out Alison Hill's "Working with Data in R"
  saved in the R folder of the RStudio project

Online Books

R for Data Science

This book will teach you how to do data science with R: You’ll learn how to get your data into R, get it into the most useful structure, transform it, visualise it and model it.

ModernDive: Statistical Inference via Data Science

This is intended to be a gentle introduction to the practice of analyzing data and answering questions using data the way data scientists, statisticians, data journalists, and other researchers would.

Data Visualization: A practical Introduction

This book is a hands-on introduction to the principles and practice of looking at and presenting data using R and ggplot.

Fundamentals of Data Visualization

The book is meant as a guide to making visualizations that accurately reflect the data, tell a story, and look professional. Even though nearly all of the figures in this book were made with R and ggplot2, this is not an R book. It focuses on the concepts and the figures, not on the code.

Open source R-based Courses

Alison Hill - Introduction to Biostatistics for the Basic Sciences - Oregon Health & Science University

Mine Cetinkaya-Rundel - Intro to Data Science - Duke

These links will take you to each relevant section in the presentation

• Home

• Tidy Data

• Data Wrangling

• Coding Style

• Datasets in R

• Dealing with Factors

• Index

• Memes

Welcome to the memer package 📦

remotes::install_github("sctyner/memer")
library(memer)

memer is a a tidyverse-compatible R package for creating memes

meme_get("OprahGiveaway") %>% 
  meme_text_bottom("EVERYONE GETS A MEME!", size = 30)

What's in the package?

meme_list()

##  [1] "AllTheThings"       "AmericanChopper"    "AncientAliens"     
##  [4] "BatmanRobin"        "DistractedBf"       "EvilKermit"        
##  [7] "ExpandingBrain"     "FirstWorldProbs"    "FryNotSure"        
## [10] "HotlineDrake"       "IsThisAPigeon"      "NoneOfMyBusiness"  
## [13] "CheersLeo"          "OneDoesNotSimply"   "DosEquisMan"       
## [16] "OffRamp"            "OprahGiveaway"      "Philosoraptor"     
## [19] "PicardFacePalm"     "PicardWTH"          "Purples"           
## [22] "PutItPatrick"       "Rainbow"            "ShiaJustDoIt"      
## [25] "Spongebob"          "SuccessKid"         "ThatWouldBeGreat"  
## [28] "TheRockDriving"     "ThinkAboutIt"       "TrumpBillSigning"  
## [31] "TwoButtonsAnxiety"  "WhatIfIToldYou"     "CondescendingWonka"
## [34] "YoDawg"             "Y-U-NOguy"

Let's make a meme

meme_get("TheRockDriving") %>% 
  meme_text_rock("Hey, how do I prep for an IRB audit?", 
                 "\nPrint, \n...everything.")

Now you try

meme_get("SuccessKid") %>% 
  meme_text_bottom("ENTER TEXT HERE")