R part I (syntax & data types)

• Open-source
• Free
• Versatile (a language, not just a statistical package)
  • Stats & plotting
  • Data cleaning & organization
  • Scripts & functions
  • Data products
• Large online user community

Swirl: free beginning through advanced lessons that you can run in RStudio

Datacamp: free introduction to R course (more advanced lessons cost $)

R for Data Science: book by Hadley Wickham that explains the "tidy data" framework we will start learning next week

RStudio is an "integrated development environment" for R. In other words, it is your interface for working with R code.

Windows within R Studio:

• Console: enter code here
• Files: shows files and directories in your working directory
• Plots: displays any plots you create
• Packages: shows available and loaded packages
• Help: shows more information about a command of interest
• Environment: displays variables and objects you have created or loaded
• Tabbed area at top left: scripts and data are displayed here

At first, we will mostly use the Console, Plots, Help, and Environment windows.

When we program, we usually need to store information in variables. In R, variables are assigned with R objects. There are several types of R objects:

• vector
• matrix
• list
• factor
• dataframe

On the next slides, we will explore each type of object.

Vectors are one-dimensional and hold elements of a single class.

(Classes in R: numeric, integer, character, logical, complex, raw)

Example of a numeric vector:

4, 18, 3, 7, 9

Example of a character vector:

Mon, today, Weds, Fri

Matrices are two-dimensional and hold elements of a single class. Arrays are multi-dimensional and hold elements of a single class.

Lists can contain elements from different classes.

[['a']] [[1, 2, 3]] [[7]] [['cat']]

Factors are vectors that contain embedded information about the unique values of the variable within the vector.

As an example, the following is a factor object:

apple pear orange pear pear apple orange pear

and R knows that the factor has 3 levels:

apple orange pear

Dataframes are two-dimensional table objects that can contain elements from different classes.

An example of a dataframe is shown below:

data_fruits; str(data_fruits)

##    fruit letters rating
## 1  apple       5    1.5
## 2 banana       6    3.0
## 3  melon       5    5.0
## 4   pear       4    3.0

## 'data.frame':    4 obs. of  3 variables:
##  $ fruit  : Factor w/ 4 levels "apple","banana",..: 1 2 3 4
##  $ letters: num  5 6 5 4
##  $ rating : num  1.5 3 5 3

• rm(list = ls()) clears your workspace
• Use the <- operator to create objects (you can also use =, but I reserve this for function arguments)
  • Example: a <- 10 assigns a value of 10 to the a object
• Call a function by enclosing its arguments in parentheses:
  • object_name <- function(input, argument = value)
• Use # at the start of a line to incude comments in your code
• Enter ? before the name of a command to open its help page
  • Example: ?mean shows the help page for the mean() function
• On a Mac, use command + Enter to run a single line or highlighted section within an R script.

Let's try some basic operations in R. Open R Studio, then open a new R script. Copy the text from the script for this lesson into the R script.