Array#intersection

array & other_array -> array

The intersection method returns a new array containing elements that appear in all the arrays. When you use the & operator, it performs the same operation between exactly two arrays.

Syntax

array & other_array
array.intersection(*other_arrays)

Parameters

Parameter	Type	Default	Description
other_array	Array	—	The array to intersect with
*other_arrays	Array	—	Additional arrays (for the method form)

Examples

Basic usage with the & operator

a = [1, 2, 3, 4, 5]
b = [3, 4, 5, 6, 7]

a & b
# => [3, 4, 5]

Using the method form with multiple arrays

a = [1, 2, 3, 4]
b = [2, 3, 5, 6]
c = [2, 3, 7, 8]

a.intersection(b, c)
# => [2, 3]

Handling duplicate values

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

a & b
# => [1, 2, 3]

The result contains each common element only once, even if it appeared multiple times in the original arrays.

Common Patterns

Filtering array contents

# Keep only elements that exist in a whitelist
allowed = [1, 2, 3]
user_input = [1, 4, 2, 5, 3, 6]

user_input & allowed
# => [1, 2, 3]

Set operations

# Find common tags between two posts
post1_tags = ["ruby", "rails", "tutorial"]
post2_tags = ["ruby", "rails", "performance"]

common = post1_tags & post2_tags
# => ["ruby", "rails"]

See Also

• Array#compact
• Array#flatten
• Array#flatten!