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.

  • 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.

Comparison

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)

Example

require 'set'
s1 = Set.new [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

Contact

- Akinori MUSHA <knu@iDaemons.org> (current maintainer)
Methods
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Included Modules
Constants
InspectKey = :__inspect_key__
 
Class Public methods
[](*ary)

Creates a new set containing the given objects.

# File lib/set.rb, line 73
def self.[](*ary)
  new(ary)
end
new(enum = nil)

Creates a new set containing the elements of the given enumerable object.

If a block is given, the elements of enum are preprocessed by the given block.

# File lib/set.rb, line 82
def initialize(enum = nil, &block) # :yields: o
  @hash ||= Hash.new(false)

  enum.nil? and return

  if block
    do_with_enum(enum) { |o| add(block[o]) }
  else
    merge(enum)
  end
end
Instance Public methods
&(enum)

Returns a new set containing elements common to the set and the given enumerable object.

Also aliased as: intersection
# File lib/set.rb, line 418
def &(enum)
  n = self.class.new
  do_with_enum(enum) { |o| n.add(o) if include?(o) }
  n
end
+(enum)
Alias for: |
-(enum)

Returns a new set built by duplicating the set, removing every element that appears in the given enumerable object.

Also aliased as: difference
# File lib/set.rb, line 411
def -(enum)
  dup.subtract(enum)
end
<(set)
Alias for: proper_subset?
<<(o)
Alias for: add
<=(set)
Alias for: subset?
==(other)

Returns true if two sets are equal. The equality of each couple of elements is defined according to Object#eql?.

# File lib/set.rb, line 436
def ==(other)
  if self.equal?(other)
    true
  elsif other.instance_of?(self.class)
    @hash == other.instance_variable_get(:@hash)
  elsif other.is_a?(Set) && self.size == other.size
    other.all? { |o| @hash.include?(o) }
  else
    false
  end
end
>(set)
Alias for: proper_superset?
>=(set)
Alias for: superset?
^(enum)

Returns a new set containing elements exclusive between the set and the given enumerable object. (set ^ enum) is equivalent to ((set | enum) - (set & enum)).

# File lib/set.rb, line 428
def ^(enum)
  n = Set.new(enum)
  each { |o| n.add(o) unless n.delete?(o) }
  n
end
add(o)

Adds the given object to the set and returns self. Use merge to add many elements at once.

Also aliased as: <<
# File lib/set.rb, line 312
def add(o)
  @hash[o] = true
  self
end
add?(o)

Adds the given object to the set and returns self. If the object is already in the set, returns nil.

# File lib/set.rb, line 320
def add?(o)
  add(o) unless include?(o)
end
classify()

Classifies the set by the return value of the given block and returns a hash of {value => set of elements} pairs. The block is called once for each element of the set, passing the element as parameter.

e.g.:

require 'set'
files = Set.new(Dir.glob("*.rb"))
hash = files.classify { |f| File.mtime(f).year }
p hash    # => {2000=>#<Set: {"a.rb", "b.rb"}>,
          #     2001=>#<Set: {"c.rb", "d.rb", "e.rb"}>,
          #     2002=>#<Set: {"f.rb"}>}
# File lib/set.rb, line 470
def classify # :yields: o
  block_given? or return enum_for(__method__)

  h = {}

  each { |i|
    (h[yield(i)] ||= self.class.new).add(i)
  }

  h
end
clear()

Removes all elements and returns self.

# File lib/set.rb, line 144
def clear
  @hash.clear
  self
end
collect!()

Replaces the elements with ones returned by collect().

Also aliased as: map!
# File lib/set.rb, line 358
def collect!
  block_given? or return enum_for(__method__)
  replace(self.class.new(self) { |o| yield(o) })
end
delete(o)

Deletes the given object from the set and returns self. Use subtract to delete many items at once.

# File lib/set.rb, line 326
def delete(o)
  @hash.delete(o)
  self
end
delete?(o)

Deletes the given object from the set and returns self. If the object is not in the set, returns nil.

# File lib/set.rb, line 333
def delete?(o)
  delete(o) if include?(o)
end
delete_if()

Deletes every element of the set for which block evaluates to true, and returns self.

# File lib/set.rb, line 339
def delete_if
  block_given? or return enum_for(__method__)
  # @hash.delete_if should be faster, but using it breaks the order
  # of enumeration in subclasses.
  select { |o| yield o }.each { |o| @hash.delete(o) }
  self
end
difference(enum)
Alias for: -
disjoint?(set)

Returns true if the set and the given set have no element in common. This method is the opposite of intersect?.

e.g.:

require 'set'
Set[1, 2, 3].disjoint? Set[3, 4] # => false
Set[1, 2, 3].disjoint? Set[4, 5] # => true
# File lib/set.rb, line 297
def disjoint?(set)
  !intersect?(set)
end
divide(&func)

Divides the set into a set of subsets according to the commonality defined by the given block.

If the arity of the block is 2, elements o1 and o2 are in common if block.call(o1, o2) is true. Otherwise, elements o1 and o2 are in common if block.call(o1) == block.call(o2).

e.g.:

require 'set'
numbers = Set[1, 3, 4, 6, 9, 10, 11]
set = numbers.divide { |i,j| (i - j).abs == 1 }
p set     # => #<Set: {#<Set: {1}>,
          #            #<Set: {11, 9, 10}>,
          #            #<Set: {3, 4}>,
          #            #<Set: {6}>}>
# File lib/set.rb, line 498
def divide(&func)
  func or return enum_for(__method__)

  if func.arity == 2
    require 'tsort'

    class << dig = {}         # :nodoc:
      include TSort

      alias tsort_each_node each_key
      def tsort_each_child(node, &block)
        fetch(node).each(&block)
      end
    end

    each { |u|
      dig[u] = a = []
      each{ |v| func.call(u, v) and a << v }
    }

    set = Set.new()
    dig.each_strongly_connected_component { |css|
      set.add(self.class.new(css))
    }
    set
  else
    Set.new(classify(&func).values)
  end
end
each(&block)

Calls the given block once for each element in the set, passing the element as parameter. Returns an enumerator if no block is given.

# File lib/set.rb, line 304
def each(&block)
  block or return enum_for(__method__) { size }
  @hash.each_key(&block)
  self
end
empty?()

Returns true if the set contains no elements.

# File lib/set.rb, line 139
def empty?
  @hash.empty?
end
flatten()

Returns a new set that is a copy of the set, flattening each containing set recursively.

# File lib/set.rb, line 198
def flatten
  self.class.new.flatten_merge(self)
end
flatten!()

Equivalent to #flatten, but replaces the receiver with the result in place. Returns nil if no modifications were made.

# File lib/set.rb, line 204
def flatten!
  replace(flatten()) if any? { |e| e.is_a?(Set) }
end
include?(o)

Returns true if the set contains the given object.

Note that include? and member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

Also aliased as: member?
# File lib/set.rb, line 214
def include?(o)
  @hash[o]
end
initialize_clone(orig)

Clone internal hash.

# File lib/set.rb, line 112
def initialize_clone(orig)
  super
  @hash = orig.instance_variable_get(:@hash).clone
end
initialize_dup(orig)

Dup internal hash.

# File lib/set.rb, line 106
def initialize_dup(orig)
  super
  @hash = orig.instance_variable_get(:@hash).dup
end
inspect()

Returns a string containing a human-readable representation of the set. (“#<Set: {element1, element2, …}>”)

# File lib/set.rb, line 532
def inspect
  ids = (Thread.current[InspectKey] ||= [])

  if ids.include?(object_id)
    return sprintf('#<%s: {...}>', self.class.name)
  end

  ids << object_id
  begin
    return sprintf('#<%s: {%s}>', self.class, to_a.inspect[1..-2])
  ensure
    ids.pop
  end
end
intersect?(set)

Returns true if the set and the given set have at least one element in common.

e.g.:

require 'set'
Set[1, 2, 3].intersect? Set[4, 5] # => false
Set[1, 2, 3].intersect? Set[3, 4] # => true
# File lib/set.rb, line 279
def intersect?(set)
  set.is_a?(Set) or raise ArgumentError, "value must be a set"
  if size < set.size
    any? { |o| set.include?(o) }
  else
    set.any? { |o| include?(o) }
  end
end
intersection(enum)
Alias for: &
keep_if()

Deletes every element of the set for which block evaluates to false, and returns self.

# File lib/set.rb, line 349
def keep_if
  block_given? or return enum_for(__method__)
  # @hash.keep_if should be faster, but using it breaks the order of
  # enumeration in subclasses.
  reject { |o| yield o }.each { |o| @hash.delete(o) }
  self
end
length()
Alias for: size
map!()
Alias for: collect!
member?(o)
Alias for: include?
merge(enum)

Merges the elements of the given enumerable object to the set and returns self.

# File lib/set.rb, line 384
def merge(enum)
  if enum.instance_of?(self.class)
    @hash.update(enum.instance_variable_get(:@hash))
  else
    do_with_enum(enum) { |o| add(o) }
  end

  self
end
proper_subset?(set)

Returns true if the set is a proper subset of the given set.

Also aliased as: <
# File lib/set.rb, line 259
def proper_subset?(set)
  case
  when set.instance_of?(self.class)
    @hash < set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size < set.size && all? { |o| set.include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
proper_superset?(set)

Returns true if the set is a proper superset of the given set.

Also aliased as: >
# File lib/set.rb, line 233
def proper_superset?(set)
  case
  when set.instance_of?(self.class)
    @hash > set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size > set.size && set.all? { |o| include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
reject!(&block)

Equivalent to #delete_if, but returns nil if no changes were made.

# File lib/set.rb, line 366
def reject!(&block)
  block or return enum_for(__method__)
  n = size
  delete_if(&block)
  self if size != n
end
replace(enum)

Replaces the contents of the set with the contents of the given enumerable object and returns self.

# File lib/set.rb, line 151
def replace(enum)
  if enum.instance_of?(self.class)
    @hash.replace(enum.instance_variable_get(:@hash))
    self
  else
    do_with_enum(enum)  # make sure enum is enumerable before calling clear
    clear
    merge(enum)
  end
end
select!(&block)

Equivalent to #keep_if, but returns nil if no changes were made.

# File lib/set.rb, line 375
def select!(&block)
  block or return enum_for(__method__)
  n = size
  keep_if(&block)
  self if size != n
end
size()

Returns the number of elements.

Also aliased as: length
# File lib/set.rb, line 133
def size
  @hash.size
end
subset?(set)

Returns true if the set is a subset of the given set.

Also aliased as: <=
# File lib/set.rb, line 246
def subset?(set)
  case
  when set.instance_of?(self.class)
    @hash <= set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size <= set.size && all? { |o| set.include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
subtract(enum)

Deletes every element that appears in the given enumerable object and returns self.

# File lib/set.rb, line 396
def subtract(enum)
  do_with_enum(enum) { |o| delete(o) }
  self
end
superset?(set)

Returns true if the set is a superset of the given set.

Also aliased as: >=
# File lib/set.rb, line 220
def superset?(set)
  case
  when set.instance_of?(self.class)
    @hash >= set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size >= set.size && set.all? { |o| include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
to_a()

Converts the set to an array. The order of elements is uncertain.

# File lib/set.rb, line 163
def to_a
  @hash.keys
end
to_set(klass = Set, *args, &block)

Returns self if no arguments are given. Otherwise, converts the set to another with klass.new(self, *args, &block).

In subclasses, returns klass.new(self, *args, &block) unless overridden.

# File lib/set.rb, line 172
def to_set(klass = Set, *args, &block)
  return self if instance_of?(Set) && klass == Set && block.nil? && args.empty?
  klass.new(self, *args, &block)
end
union(enum)
Alias for: |
|(enum)

Returns a new set built by merging the set and the elements of the given enumerable object.

Also aliased as: +, union
# File lib/set.rb, line 403
def |(enum)
  dup.merge(enum)
end