Array

Array.new, []

Returns: Array · Updated March 13, 2026 · Kernel Methods

arrays collections ordered indexed

The Array class is Ruby’s primary ordered collection. Arrays can hold objects of any type and grow dynamically. They are one of the most frequently used data structures.

Creating Arrays

# Literal syntax
arr = [1, 2, 3]
arr = []  # Empty array

# With Array.new
arr = Array.new(3)        # => [nil, nil, nil]
arr = Array.new(3, 0)     # => [0, 0, 0]
arr = Array.new(3) { |i| i }  # => [0, 1, 2]

# From other objects
Array("hello")  # => ["hello"]
Array(1..5)     # => [1, 2, 3, 4, 5]

Accessing Elements

arr = [:a, :b, :c, :d]

arr[0]     # => :a (first)
arr[-1]    # => :d (last)
arr[1, 2]  # => [:b, :c] (slice)
arr.first  # => :a
arr.last   # => :d

Modification

arr = [1, 2, 3]

arr << 4        # => [1, 2, 3, 4] (push)
arr.push(5)     # => [1, 2, 3, 4, 5]
arr.pop         # => 5, arr is [1, 2, 3, 4]
arr.shift       # => 1, arr is [2, 3, 4]
arr.unshift(0)  # => [0, 1, 2, 3, 4]

Iteration

[1, 2, 3].each { |i| puts i }
[1, 2, 3].map { |i| i * 2 }     # => [2, 4, 6]
[1, 2, 3].select { |i| i > 1 } # => [2, 3]
[1, 2, 3].reduce(:+)            # => 6

Useful Methods

arr = [1, 2, 3, 2, 1]

arr.length      # => 5
arr.size        # => 5
arr.empty?      # => false
arr.include?(2) # => true
arr.index(2)    # => 1
arr.count(2)    # => 2
arr.uniq        # => [1, 2, 3]
arr.sort        # => [1, 1, 2, 2, 3]
arr.reverse     # => [1, 2, 3, 2, 1]

Practical Examples

Queue

queue = []
queue << item
item = queue.shift

Stack

stack = []
stack.push(item)
item = stack.pop

Set-like Operations

a = [1, 2, 3]
b = [2, 3, 4]

a | b   # => [1, 2, 3, 4] (union)
a & b   # => [2, 3] (intersection)
a - b   # => [1] (difference)

Matrix Representation

matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]

matrix[1][1]  # => 5 (center)

Comprehension-style

# Like list comprehension in Python
arr = (1..5).to_a.select { |x| x.even? }  # => [2, 4]
squares = (1..5).map { |x| x*x }           # => [1, 4, 9, 16, 25]

Arrays are versatile, efficient for indexed access, and form the foundation of many Ruby programs.