Ruby Arrays and Hashes

In Ruby, an array is an ordered collection of objects, which can hold multiple data types, including numbers, strings, other arrays, or even objects. Of the languages we’ve looked at, it is most similar to lists in Python, where you can store dynamic types, and they are dynamically sized.

There are a couple of ways you can create an array, including by giving it values, as well as creating an empty array:

# Using square brackets
numbers = [1, 2, 3, 4, 5]

# Using Array.new
empty_array = Array.new

# Using Array.new with a set of default values
array_with_defaults = Array.new(3, "default") # ["default", "default", "default"]

Accessing elements is fairly straightforward if you have worked with a language like Python. You can use either positive or negative indexes. If you use a positive index, the first element is 0, as is a zero based numbering system.

letters = ['a', 'b', 'c']

letters[0]
# 'a'

letters[1]
# 'b'

letters[-1]
# 'c'

If you go outside the size of the array, you will get a nil value returned to you.

Adding New Elements to an Array

numbers.push(6)    # => [1, 2, 3, 4, 5, 6]
numbers << 7       # => [1, 2, 3, 4, 5, 6, 7]
numbers.unshift(0) # => [0, 1, 2, 3, 4, 5, 6, 7]

Notice that unshift puts the value at the beginning of the array.

Removing Elements from and Array

letters.pop    # Removes the last element
letters.shift  # Removes the first element
letters.delete("b") # Deletes the element with a value `b`

Searching an Array

You can easily search for an element in an array, unlike some languages where you’d have to build that feature yourself, in Ruby, it’s provided for you.

numbers.include?(3) # => true

Other things you can do

There are other methods you can use such as:

• flatten – merge nested arrays into a single array
• sort – sort the elements of an array
• uniq – find the unique elements of an array

Hashes in Ruby

In Ruby, hashes are collections of key-value pairs, similar to dictionaries or maps in other languages.

While they might seem similar to arrays in many ways, they differ significantly from arrays in how they organize and access data.

Key Features of Hashes:

Feature	Array	Hash
Structure	Ordered list of elements	Key-value pairs
Access by	Integer-based index, Indexes start at zero	Key (any object can be a key)
Use Case	Ordered collections or lists	Lookup tables or dictionaries
Example	[1, 2, 3]	{ name: "Alice", age: 25 }

---

Accessing Data

Access values by their keys.

hash = { name: "Alice", age: 25 } 
hash[:name] # => "Alice"

---

Adding/Updating Elements:

Add or update key-value pairs.

hash[:city] = "New York" 
hash # => { name: "Alice", age: 25, city: "New York" }

---

Iteration:

Use methods like each to iterate over keys and values.

 hash.each { |key, value| puts "#{key}: #{value}" }

---

When to Use a Hash:

Use hashes when you need to associate keys with values, such as:

• Storing attributes about something, but don’t want to use a class: user = { name: "Alice", age: 25, city: "New York" }
• Configuration settings: config = { theme: "dark", language: "en", timezone: "UTC" }
• Lookup tables: status_codes = { 200 => "OK", 404 => "Not Found", 500 => "Internal Server Error" }

Ruby Arrays and Hashes was originally found on Access 2 Learn