Arrays

Learning Goals

• Understand how to declare variables that store Arrays
• Understand how to access elements within an Array
• Use basic Array methods to manipulate data in Arrays

Vocabulary

• Array: a Data Type that allows us to store multiple pieces of data in one variable
• bracket notation: the syntax for accessing elements in an Array
• element: a piece of data in an Array
• index position: the location of an element in an Array
• method: a piece of functionality that is built into the Ruby language
• square brackets []: the syntax for accessing elements in an Array

Arrays

Let’s consider a list of students in a class, using the programming tools we’ve learned thus far:

student1 = "Josiah"
student2 = "Cindy"
student3 = "Violet"
student4 = "Jhun"
# on and on.

As the list of students inevitably changes and grows, this is difficult to maintain programmatically. If we wanted to send an email to every student or perform any other task for every student, we would have to write code for each, individual student, which defeats the purpose of having a computer program automate tasks.

An Array is a Data Type that allows us to store multiple pieces of data in one variable. They can be compared to lists. The Array is an incredibly powerful and necessary Data Type for building web applications.

Thinking back to the Populi platform that helped you enroll at Turing, many Arrays are used to power its functionality:

• student roster - list of all names in a given cohort
• course catalog - list of all courses we offer

Notice that in the previous examples, the items in a given list are all of the same type.

Array Syntax

• An Array is declared with the square brackets (they can be typed with the keys to the right of the p character on your keyboard).
• Each piece of data in an Array is referred to as an element.
• Elements should be separated with a comma and space.
• An Array can hold any number of elements.

students = ["Cindy", "Josiah", "Rigo"]

To describe what the previous line of code does, one might say, “The students variable stores an Array of Strings representing student names. This array has 3 elements.”

var students = ["Cindy", "Josiah", "Rigo"]

  ticket_prices = [87, 67, 99, 90, 87]

Best Practices for Arrays

Here are some best practices for Arrays in software development:

1. The name of a variable that stores an Array should usually be plural to indicate that it has the potential to hold many elements of that type.
2. While Ruby technically allows an Array to hold multiple Data Types, it is not best practice and in any real-world application, will usually be unhelpful anyways.

Accessing Elements within an Array

To access one element from an array we use bracket notation and a number that corresponds with that element. That number is referred to as an index position. As weird as it may seem, counting starts with 0 in most programming languages.

Through reading the code snippets below, one can infer that the first element is in index position 0, and counting increments by 1.

# in irb
students = ["Cindy", "Josiah", "Rigo"]

students[0]
# --> "Cindy"

students[2]
# --> "Rigo"

# in VS Code, when running the file in the command line
students = ["Cindy", "Josiah", "Rigo"]

puts students[0]
# --> "Cindy"

puts students[2]
# --> "Rigo"

var students = ["Cindy", "Josiah", "Rigo"]

console.log(students[0])
// --> "Cindy"

console.log(students[2])
// --> "Rigo"

Storing Arrays, Accessing Elements

ticket_prices = [87, 67, 99, 90, 87]

Additional Practice

Extension

It is highly recommended that you complete the work below later this evening. Although there are no deliverables, please reach out if you do have any questions about Array methods.

Array Methods

Developers often need to modify data in an Array. Today, we’ll explore several Array methods in Ruby. These methods are built-in functionalities designed for Arrays, each performing a specific task. While you will memorize some commonly used methods, others can be referenced in documentation as needed.

Array Methods Syntax

To use an Array method in Ruby, we first must tell Ruby which Array we want to perform the method on. After that, a dot or period (called dot syntax), followed by the name of the method.

students = ["Cindy", "Josiah", "Rigo"]
students.pop

p students

To describe what the previous line of code does, one might say, “This line of code calls the pop method on the students Array.”

var students = ["Cindy", "Josiah", "Rigo"]

students.pop()

console.log(students)

Learning From Reading Code You Don’t Know

As a developer, an important skillset is researching and reading documentation (and to note, in many cases, documentation is not always current, rarely perfect, and usually quite dense).

Since researching and reading documentation can sometimes be time-consuming, another skill is to be able to make the decision about when it’s time to go to Google. In this activity, you will be provided with some structure to teach yourself a few technical concepts. The main goal is not to learn the technical concepts, it’s to practice and explore strategies to learn in an environment such as this, and how to make the decision about what to do when you need to learn something.