Array#compact

arr.compact -> array

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

arrays compact nil enumerable

Array#compact removes all nil values from an array and returns a new array. This is useful for cleaning up data after operations that may produce nil values, such as array indexing or mapping.

Syntax

arr.compact
arr.compact!

The method without a bang (compact) returns a new array. The bang version (compact!) modifies the array in place and returns the array itself.

Parameters

This method takes no parameters.

Examples

Basic usage

# Remove nil values from an array
array = [1, nil, 2, nil, 3]
array.compact
# => [1, 2, 3]

# Original array is unchanged
array
# => [1, nil, 2, nil, 3]

Destructive version

# compact! modifies in place
array = [1, nil, 2, nil, 3]
array.compact!
# => [1, 2, 3]

# Now the original is modified
array
# => [1, 2, 3]

With mixed values

# Works with any object types
data = ["hello", nil, 42, nil, :symbol, [1, 2], nil]
data.compact
# => ["hello", 42, :symbol, [1, 2]]

After mapping

# Common pattern: compact after map that can return nil
numbers = [1, 2, 3, 4, 5]
squared_evens = numbers.map { |n| n ** 2 if n.even? }
# => [nil, 4, nil, 16, nil]

squared_evens.compact
# => [4, 16]

Common Patterns

Cleaning database results

# Simulating database query results
users = [
  { name: "Alice", email: nil },
  { name: "Bob", email: "bob@example.com" },
  { name: nil, email: "charlie@example.com" }
]

users.map { |u| u[:email] }.compact
# => ["bob@example.com", "charlie@example.com"]

Filtering while preserving order

# Keep first non-nil value
values = [nil, nil, "found", nil]
values.compact.first
# => "found"

Error Cases

The method never raises an error. It works on any array:

# Empty array
[].compact
# => []

# Array with no nils
[1, 2, 3].compact
# => [1, 2, 3]

# All nils
[nil, nil].compact
# => []