Part of standard library. You need to require 'set' before using.

Set implements a collection of unordered values with no duplicates. This is a hybrid of Array’s intuitive inter-operation facilities and Hash’s fast lookup.

Set is easy to use with Enumerable objects (implementing each). Most of the initializer methods and binary operators accept generic Enumerable objects besides sets and arrays. An Enumerable object can be converted to Set using the to_set method.

Set uses Hash as storage, so you must note the following points:

  • Equality of elements is determined according to Object#eql? and Object#hash. Use Set#compare_by_identity to make a set compare its elements by their identity.

  • Set assumes that the identity of each element does not change while it is stored. Modifying an element of a set will render the set to an unreliable state.

  • When a string is to be stored, a frozen copy of the string is stored instead unless the original string is already frozen.


The comparison operators <, >, <=, and >= are implemented as shorthand for the {proper_,}{subset?,superset?} methods. However, the <=> operator is intentionally left out because not every pair of sets is comparable ({x, y} vs. {x, z} for example).


require 'set'
s1 = Set[1, 2]                        #=> #<Set: {1, 2}>
s2 = [1, 2].to_set                    #=> #<Set: {1, 2}>
s1 == s2                              #=> true
s1.add("foo")                         #=> #<Set: {1, 2, "foo"}>
s1.merge([2, 6])                      #=> #<Set: {1, 2, "foo", 6}>
s1.subset?(s2)                        #=> false
s2.subset?(s1)                        #=> true

Set Reference


SortedSet implements a Set that guarantees that its elements are yielded in sorted order (according to the return values of their #<=> methods) when iterating over them.

All elements that are added to a SortedSet must respond to the <=> method for comparison.

Also, all elements must be mutually comparable: el1 <=> el2 must not return nil for any elements el1 and el2, else an ArgumentError will be raised when iterating over the SortedSet.


require "set"

set =[2, 1, 5, 6, 4, 5, 3, 3, 3])
ary = []

set.each do |obj|
  ary << obj

p ary # => [1, 2, 3, 4, 5, 6]

set2 =[1, 2, "3"])
set2.each { |obj| } # => raises ArgumentError: comparison of Fixnum with String failed

SortedSet Reference