Ruby Arrays (versus JavaScript Arrays)

Instructions

Fork, clone, branch (training), bundle install

Objectives

By the end of this, students should be able to:

Contrast Ruby Arrays with JavaScript Arrays.
Create a Ruby Array using both the literal ([]) and new constructors.
Assign an element at a specific index in a Ruby Array.
Access elements by index in a Ruby Array.
Add elements to and remove elements from the end of a Ruby Array.
Add elements to and remove elements from the beginning of a Ruby Array.

Introduction

In Ruby, "Arrays are ordered, integer-indexed collections of any object." From that, Ruby Arrays seem a lot like JavaScript Arrays. But there are some important differences.

Creating a Ruby Array

As with JavaScript, Ruby Arrays can be created using literals (technically, a constructor method on class Array) and with a constructor.

Demonstration

> developers = []
=> []
> developers = Array.new
=> []

With the literal syntax, we can create an array with initial values.

> not_the_same_type = [[], 'one', 2.0, 3]
=> [[], "one", 2.0, 3]
> developers = ['Roberto', 'Ben', 'Susan', 'Nick']
=> ["Roberto", "Ben", "Susan", "Nick"]

If all of the entries are strings, Ruby provides a (Perl inspired) string quoting mechanism to create an Array.

> developers = %w{Roberto Ben Susan Nick}
=> ["Roberto", "Ben", "Susan", "Nick"]

Code along

Let's use Array::new to create some initialized arrays in bin/code_along.rb. Creating Arrays has an important caveat when creating Ruby Arrays with default values.

Create an empty array, lit_array, using the literal syntax
Create an array, constr_array, using the constructor syntax, initialized with 5 elements
Create an array, ten_false_array, initialized with 10 false elements

How does this compare with creating JavaScript Arrays?

Lab 1

In bin/lab.rb use a block initializer with Array.new to create a Ruby Array with ten elements where elements are equal to their index multiplied by 2. Store the result and display it on the console with p <array name>.

In bin/lab.js do the same in JavaScript with new Array and a method chain.

Assigning and accessing elements in a Ruby Array

Demonstration

Let's explore:

Array#[] (Element Reference)
Array#[]= (Element Assignment)

> developers[0]
=> "Roberto"
developers[-1]
=> "Nick"
> developers[-4] == developers[0]
=> true
> developers[developers.length]
=> nil
> developers[-5]
=> nil
> developers[-3, 2]
=> ["Ben", "Susan"]
> developers[-5] = 'Jessica'
IndexError: index -5 too small for array; minimum: -4
from (pry):4:in ``__pry__''
> developers[developers.length] = 'Jessica'
=> "Jessica"

Lab 2

Working in bin/lab.rb (storing the results of any access in tmp for display):

Assign 20 to the element at length+1.
Access the 3rd element from the end of an array length of 5.
Access element 9 for a length of 5 elements.
Assign [-12, -49] to the 5th element from the end for a length of 3.
Access all the elements starting at index 1.

In bin/lab.js do the same in JavaScript.

Using a Ruby Array as a stack or queue

Demonstration

Let's explore

Array#push (Append - also Array#<<)
Array#pop (Remove from end)
Array#unshift (Prepend)
Array#shift (Remove from beginning)

> developers << "Lou"
=> ["Roberto", "Ben", "Susan", "Nick", "Jessica", "Lou"]
> developers.push "Vince"
=> ["Roberto", "Ben", "Susan", "Nick", "Jessica", "Lou", "Vince"]
> developers << "Natalie" << "Phil"
=> ["Roberto",
 "Ben",
 "Susan",
 "Nick",
 "Jessica",
 "Lou",
 "Vince",
 "Natalie",
 "Phil"]
> developers.shift 4
=> ["Roberto", "Ben", "Susan", "Nick"]
> developers
=> ["Jessica", "Lou", "Vince", "Natalie", "Phil"]

Lab

In lab.md describe the differences between the Array methods push, pop, unshift, and shift in Ruby and JavaScript.

natdjerf/ruby-vs-js-arrays

Ruby Arrays (versus JavaScript Arrays)

Instructions

Objectives

Introduction

Creating a Ruby Array

Demonstration

Code along

Lab 1

Assigning and accessing elements in a Ruby Array

Demonstration

Lab 2

Using a Ruby Array as a stack or queue

Demonstration

Lab

License