Array#rotate

Added in v1.9.2 · Updated March 13, 2026 · Array Methods

ruby array rotate

.rotate and .rotate! shift array elements by moving the element at a given index to the front, wrapping elements from the beginning to the end.

Brief Intro

rotate creates a new array with elements rearranged. rotate! modifies the original array in place. Both methods are useful for cycling through queue-like data structures or creating rotating schedules.

Signature

Method	Parameters	Return Type
`rotate`	`cnt = 1` (Integer)	Array
`rotate!`	`cnt = 1` (Integer)	Array (self)

Parameter Details:

cnt — The zero-based index of the element that should become the first element. Default is 1. Negative counts rotate in the opposite direction.

Code Examples

Basic Rotation

array = [1, 2, 3, 4, 5]

array.rotate
# => [2, 3, 4, 5, 1]

array
# => [1, 2, 3, 4, 5]  (original unchanged)

Rotate with Custom Count

array = [1, 2, 3, 4, 5]

array.rotate(2)
# => [3, 4, 5, 1, 2]

array.rotate(0)
# => [1, 2, 3, 4, 5]  (no rotation)

array.rotate(5)
# => [1, 2, 3, 4, 5]  (full cycle)

Negative Rotation

array = [1, 2, 3, 4, 5]

array.rotate(-1)
# => [5, 1, 2, 3, 4]

array.rotate(-2)
# => [4, 5, 1, 2, 3]

In-Place Rotation with `rotate!`

array = [1, 2, 3, 4, 5]

array.rotate!
# => [2, 3, 4, 5, 1]

array
# => [2, 3, 4, 5, 1]  (original modified)

array.rotate!(3)
# => [5, 1, 2, 3, 4]

array
# => [5, 1, 2, 3, 4]

Practical Use: Round-Robin Scheduling

players = ["Alice", "Bob", "Charlie", "Diana"]

# Generate schedule for 4 rounds
4.times do |round|
  puts "Round #{round + 1}: #{players.join(' vs ')}"
  players.rotate!
end

# Output:
# Round 1: Alice vs Bob vs Charlie vs Diana
# Round 2: Bob vs Charlie vs Diana vs Alice
# Round 3: Charlie vs Diana vs Alice vs Bob
# Round 4: Diana vs Alice vs Bob vs Charlie

Return Value

rotate returns a new array containing the rotated elements. The original array remains unchanged.
rotate! returns self (the modified array), allowing method chaining.
When cnt equals the array length, the returned array equals the original.

Edge Cases

Empty array returns a new empty array.
Single-element array returns itself (new array for rotate, same for rotate!).

[].rotate
# => []

[].rotate!
# => []

[42].rotate
# => [42]

[42].rotate!
# => [42]