Introduction to Scope and Methods

Sam Frederick

5/22/23

Installing R and RStudio

  • Navigate to https://posit.co/download/rstudio-desktop/
    • Can also just search for RStudio Desktop
  • Follow the download instructions
    1. Download R
    2. Download RStudio

Installing R and RStudio

Working Directories

  • Important!

  • Create a folder for this course on your computer

  • Give it a short and meaningful title (e.g., Scope and Methods)

  • Store your data, R files, and any other helpful info from the course in it

  • Know where it is located (i.e., know the path)

Working Directories

Example Paths to Folders:

  • Mac:
    • “/Users/samfrederick/Desktop/Scope and Methods”
    • “~/Desktop/Scope and Methods”
  • Windows:
    • “C://Users/samfrederick/Desktop/Scope and Methods”

Working Directories

  • Depending on your preferences, you can:
    • Specify the path to your file manually
    • Set your working directory manually
    • Use an RProject and associate it with your course folder

Manual Path Specification

  • Not recommended
    • lengthy, error-prone, not very replicable
  • Write out full path of file:
    • e.g., “/Users/samfrederick/Desktop/Scope and Methods/file.csv”

Setting Working Directory Manually

  • Better but still can have issues with replication and lengthiness

  • Use the R command setwd() to specify the “working directory”

    • i.e., your course folder
    • Only need to do this once in a given R session
setwd("/Users/samfrederick/Desktop/Scope and Methods/")

RProjects

  • Best method

  • “File” > “New Project” > “Existing Directory” > “Browse” > “Create Project”

  • Only need to open project to access your files

Overview of R

Top Left: Usually RScripts/RMarkdown files

Overview of R

Top Right: Environment where loaded objects will be shown

Overview of R

Bottom Left: Console (can run code–but this will not necessarily be as reproducible)

Overview of R

Bottom Right: Plots, Help, Files in Working Directory

RScript

  • As (social) scientists, we want our work to be reproducible

  • Important to save work such that another person could follow your exact steps and would get the same results

  • Use RScript files to write and save code

    • Like Word documents, but for R code

RScript

RScript

RScript

RScript: Running Code

  • command + return on a Mac or control + Enter on a Windows

RMarkdown

  • Similar to RScript files

  • But also allows you to include text

  • Produces good output for Problem Sets

RMarkdown

RMarkdown

  • Select HTML or Word (have to install LaTeX to use PDF)

RMarkdown

RMarkdown Advice

  • Knit your RMarkdown frequently (i.e., at each step of creation)

  • Often small errors can cause issues

    • And can be hard to catch otherwise

RMarkdown Practice

  • Open RStudio

  • Try to open a new RMarkdown document

  • Which parts of the document seem to include R code?

  • See if you can figure out how to insert a new code chunk (a section that R reads as code)

RMarkdown: Running Code

  • command + return on a Mac or control + Enter on a Windows

RMarkdown: Running Code

Intro to Coding in R

Arithmetic:

  • Addition: +

  • Subtraction: -

  • Multiplication: *

  • Division: /

  • Exponents: x^y (x to the power of y)

Intro to Coding in R: Practice

  • Go to R and open an RScript file

  • Set your working directory to your course folder by writing out code in the RScript

setwd("/Users/samfrederick/Desktop/Scope and Methods")

Intro to Coding in R

What is the output of the following lines of code?

2+2
2+2-3
2+2-3*4
2+2-3*4/6
(2+2-3*4/6)^3
2+2
[1] 4
2+2-3
[1] 1
2+2-3*4
[1] -8
2+2-3*4/6
[1] 2
(2+2-3*4/6)^3
[1] 8

Functions in R

Standard format:

  • functionname(argumentname = argument)

Function help:

  • Type “?functionname” and run that line of code

    • Help page will pop up in the “Help” pane

    . . .

    • Help pages usually have overviews of the function, descriptions of key arguments, outputs, and example code

Basic Functions

  • Addition: sum()

    • e.g., sum(1, 2)

  • Average: mean()

  • Square Root: sqrt()

  • Minimum: min(); Maximum: max()

Basic Functions

Try running the following code:

9+8+157.5
[1] 174.5

How would you calculate this value using an R function?

What is the average of these three numbers?

Basic Functions: Vectors

  • Concatenate: c() (turns a comma separated list of numbers into a vector)
    • Vectors of numbers can be passed to functions
mean(c(1,2,3))
[1] 2

  • Determine length of vector: length()

  • Return unique items in vector: unique()

More Functions and Operators

  • begin:end: creates a vector containing the sequence of integers from begin to end

  • seq(a, b, by = c): creates a vector containing the sequence of integers from a to b in steps of size c

1:3
[1] 1 2 3
seq(1,3, by = 1)
[1] 1 2 3
mean(seq(2, 20, by = 2))
[1] 11

Assignment Operator

  • x <- y: assign y to object x
x <- 1:5
mean(x)
[1] 3
sum(x)
[1] 15
y <- sum(x)
y
[1] 15

Loading Data into R

  • Mostly work with csv files (similar to Excel spreadsheets)

  • Load with some variant of read.csv() function

  • This is where setting your working directory becomes important

data <- read.csv("example_data.csv")
  • Data loaded in as a data.frame object in R
    • Columns are variables and rows are individual observations

Recap

  • Set working directory to course folder:
    • setwd(path/to/course folder)
    • Use an RProject associated with course folder
  • Write (and save) code in RScripts or RMarkdown files
    • Knit RMarkdown files frequently after changes to catch bugs in code early
    • RMarkdown will be super helpful for problem sets

Getting Help

  • Section

  • Other students

  • ? operator in RStudio (run ?functionname)

  • stackoverflow.com

  • I’m also happy to meet or to answer questions over email

    • sdf2128@columbia.edu

Next Section:

  • Types of objects in R

  • If statements

  • Summarizing data

  • Missing data

  • For loops

Introduction to R