class Set

This library provides the Set class, which implements a collection of unordered values with no duplicates. It is a hybrid of Array’s intuitive inter-operation facilities and Hash’s fast lookup.

The method to_set is added to Enumerable for convenience.

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.

Comparison¶ ↑

The comparison operators <, >, <=, and >= are implemented as shorthand for the {proper_,}{subset?,superset?} methods. The <=> operator reflects this order, or return nil for sets that both have distinct elements ({x, y} vs. {x, z} for example).

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

Contact¶ ↑

Akinori MUSHA <knu@iDaemons.org> (current maintainer)

What’s Here¶ ↑

First, what’s elsewhere. Class Set:

Inherits from class Object.
Includes module Enumerable, which provides dozens of additional methods.

In particular, class Set does not have many methods of its own for fetching or for iterating. Instead, it relies on those in Enumerable.

Here, class Set provides methods that are useful for:

Creating a Set
Set Operations
Comparing
Querying
Assigning
Deleting
Converting
Iterating
And more.…

Methods for Creating a Set¶ ↑

::[]: Returns a new set containing the given objects.
::new: Returns a new set containing either the given objects (if no block given) or the return values from the called block (if a block given).

Methods for Set Operations¶ ↑

| (aliased as union and +): Returns a new set containing all elements from self and all elements from a given enumerable (no duplicates).
& (aliased as intersection): Returns a new set containing all elements common to self and a given enumerable.
- (aliased as difference): Returns a copy of self with all elements in a given enumerable removed.
^: Returns a new set containing all elements from self and a given enumerable except those common to both.

Methods for Comparing¶ ↑

<=>: Returns -1, 0, or 1 as self is less than, equal to, or greater than a given object.
==: Returns whether self and a given enumerable are equal, as determined by Object#eql?.
compare_by_identity?: Returns whether the set considers only identity when comparing elements.

Methods for Querying¶ ↑

length (aliased as size): Returns the count of elements.
empty?: Returns whether the set has no elements.
include? (aliased as member? and ===): Returns whether a given object is an element in the set.
subset? (aliased as <=): Returns whether a given object is a subset of the set.
proper_subset? (aliased as <): Returns whether a given enumerable is a proper subset of the set.
superset? (aliased as >=]): Returns whether a given enumerable is a superset of the set.
proper_superset? (aliased as >): Returns whether a given enumerable is a proper superset of the set.
disjoint?: Returns true if the set and a given enumerable have no common elements, false otherwise.
intersect?: Returns true if the set and a given enumerable: have any common elements, false otherwise.
compare_by_identity?: Returns whether the set considers only identity when comparing elements.

Methods for Assigning¶ ↑

add (aliased as <<): Adds a given object to the set; returns self.
add?: If the given object is not an element in the set, adds it and returns self; otherwise, returns nil.
merge: Merges the elements of each given enumerable object to the set; returns self.
replace: Replaces the contents of the set with the contents of a given enumerable.

Methods for Deleting¶ ↑

clear: Removes all elements in the set; returns self.
delete: Removes a given object from the set; returns self.
delete?: If the given object is an element in the set, removes it and returns self; otherwise, returns nil.
subtract: Removes each given object from the set; returns self.
delete_if - Removes elements specified by a given block.
select! (aliased as filter!): Removes elements not specified by a given block.
keep_if: Removes elements not specified by a given block.
reject! Removes elements specified by a given block.

Methods for Converting¶ ↑

classify: Returns a hash that classifies the elements, as determined by the given block.
collect! (aliased as map!): Replaces each element with a block return-value.
divide: Returns a hash that classifies the elements, as determined by the given block; differs from classify in that the block may accept either one or two arguments.
flatten: Returns a new set that is a recursive flattening of self. flatten!: Replaces each nested set in self with the elements from that set.
inspect (aliased as to_s): Returns a string displaying the elements.
join: Returns a string containing all elements, converted to strings as needed, and joined by the given record separator.
to_a: Returns an array containing all set elements.
to_set: Returns self if given no arguments and no block; with a block given, returns a new set consisting of block return values.

Methods for Iterating¶ ↑

each: Calls the block with each successive element; returns self.

Other Methods¶ ↑

reset: Resets the internal state; useful if an object has been modified while an element in the set.

Constants

VERSION

Public Class Methods

[] (*ary)

Creates a new set containing the given objects.

Set[1, 2]                   # => #<Set: {1, 2}>
Set[1, 2, 1]                # => #<Set: {1, 2}>
Set[1, 'c', :s]             # => #<Set: {1, "c", :s}>

# File lib/set.rb, line 228
def self.[](*ary)
  new(ary)
end

json_create (object)

See as_json.

# File ext/json/lib/json/add/set.rb, line 9
def self.json_create(object)
  new object['a']
end

new (enum = nil) { |o| ... }

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.

Set.new([1, 2])                       #=> #<Set: {1, 2}>
Set.new([1, 2, 1])                    #=> #<Set: {1, 2}>
Set.new([1, 'c', :s])                 #=> #<Set: {1, "c", :s}>
Set.new(1..5)                         #=> #<Set: {1, 2, 3, 4, 5}>
Set.new([1, 2, 3]) { |x| x * x }      #=> #<Set: {1, 4, 9}>

# File lib/set.rb, line 243
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

Public Instance Methods

& (enum)

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

Set[1, 3, 5] & Set[3, 2, 1]             #=> #<Set: {3, 1}>
Set['a', 'b', 'z'] & ['a', 'b', 'c']    #=> #<Set: {"a", "b"}>

# File lib/set.rb, line 640
def &(enum)
  n = self.class.new
  if enum.is_a?(Set)
    if enum.size > size
      each { |o| n.add(o) if enum.include?(o) }
    else
      enum.each { |o| n.add(o) if include?(o) }
    end
  else
    do_with_enum(enum) { |o| n.add(o) if include?(o) }
  end
  n
end

Also aliased as: intersection

+ (enum)

Alias for: |

- (enum)

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

Set[1, 3, 5] - Set[1, 5]                #=> #<Set: {3}>
Set['a', 'b', 'z'] - ['a', 'c']         #=> #<Set: {"b", "z"}>

# File lib/set.rb, line 630
def -(enum)
  dup.subtract(enum)
end

Also aliased as: difference

< (set)

Alias for: proper_subset?

<< (o)

Alias for: add

<= (set)

Alias for: subset?

<=> (set)

Returns 0 if the set are equal, -1 / +1 if the set is a proper subset / superset of the given set, or nil if they both have unique elements.

# File lib/set.rb, line 453
def <=>(set)
  return unless set.is_a?(Set)

  case size <=> set.size
  when -1 then -1 if proper_subset?(set)
  when +1 then +1 if proper_superset?(set)
  else 0 if self.==(set)
  end
end

== (other)

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

Set[1, 2] == Set[2, 1]                       #=> true
Set[1, 3, 5] == Set[1, 5]                    #=> false
Set['a', 'b', 'c'] == Set['a', 'c', 'b']     #=> true
Set['a', 'b', 'c'] == ['a', 'c', 'b']        #=> false

# File lib/set.rb, line 674
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

=== (o)

Returns true if the given object is a member of the set, and false otherwise.

Used in case statements:

require 'set'

case :apple
when Set[:potato, :carrot]
  "vegetable"
when Set[:apple, :banana]
  "fruit"
end
# => "fruit"

Or by itself:

Set[1, 2, 3] === 2   #=> true
Set[1, 2, 3] === 4   #=> false

Alias for: include?

> (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)).

Set[1, 2] ^ Set[2, 3]                   #=> #<Set: {3, 1}>
Set[1, 'b', 'c'] ^ ['b', 'd']           #=> #<Set: {"d", 1, "c"}>

# File lib/set.rb, line 661
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.

Set[1, 2].add(3)                    #=> #<Set: {1, 2, 3}>
Set[1, 2].add([3, 4])               #=> #<Set: {1, 2, [3, 4]}>
Set[1, 2].add(2)                    #=> #<Set: {1, 2}>

# File lib/set.rb, line 511
def add(o)
  @hash[o] = true
  self
end

Also aliased as: <<

add? (o)

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

Set[1, 2].add?(3)                    #=> #<Set: {1, 2, 3}>
Set[1, 2].add?([3, 4])               #=> #<Set: {1, 2, [3, 4]}>
Set[1, 2].add?(2)                    #=> nil

# File lib/set.rb, line 523
def add?(o)
  add(o) unless include?(o)
end

as_json (*)

Methods Set#as_json and Set.json_create may be used to serialize and deserialize a Set object; see Marshal.

Method Set#as_json serializes self, returning a 2-element hash representing self:

require 'json/add/set'
x = Set.new(%w/foo bar baz/).as_json
# => {"json_class"=>"Set", "a"=>["foo", "bar", "baz"]}

Method JSON.create deserializes such a hash, returning a Set object:

Set.json_create(x) # => #<Set: {"foo", "bar", "baz"}>

# File ext/json/lib/json/add/set.rb, line 28
def as_json(*)
  {
    JSON.create_id => self.class.name,
    'a'            => to_a,
  }
end

classify () { |o| ... }

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.

require 'set'
files = Set.new(Dir.glob("*.rb"))
hash = files.classify { |f| File.mtime(f).year }
hash       #=> {2000=>#<Set: {"a.rb", "b.rb"}>,
           #    2001=>#<Set: {"c.rb", "d.rb", "e.rb"}>,
           #    2002=>#<Set: {"f.rb"}>}

Returns an enumerator if no block is given.

# File lib/set.rb, line 743
def classify # :yields: o
  block_given? or return enum_for(__method__) { size }

  h = {}

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

  h
end

clear ()

Removes all elements and returns self.

set = Set[1, 'c', :s]             #=> #<Set: {1, "c", :s}>
set.clear                         #=> #<Set: {}>
set                               #=> #<Set: {}>

# File lib/set.rb, line 316
def clear
  @hash.clear
  self
end

collect! () { |o| ... }

Replaces the elements with ones returned by collect(). Returns an enumerator if no block is given.

# File lib/set.rb, line 564
def collect!
  block_given? or return enum_for(__method__) { size }
  set = self.class.new
  each { |o| set << yield(o) }
  replace(set)
end

Also aliased as: map!

compare_by_identity ()

Makes the set compare its elements by their identity and returns self. This method may not be supported by all subclasses of Set.

# File lib/set.rb, line 257
def compare_by_identity
  if @hash.respond_to?(:compare_by_identity)
    @hash.compare_by_identity
    self
  else
    raise NotImplementedError, "#{self.class.name}\##{__method__} is not implemented"
  end
end

compare_by_identity? ()

Returns true if the set will compare its elements by their identity. Also see Set#compare_by_identity.

# File lib/set.rb, line 268
def compare_by_identity?
  @hash.respond_to?(:compare_by_identity?) && @hash.compare_by_identity?
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 529
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 536
def delete?(o)
  delete(o) if include?(o)
end

delete_if (&block)

Deletes every element of the set for which block evaluates to true, and returns self. Returns an enumerator if no block is given.

# File lib/set.rb, line 543
def delete_if(&block)
  block_given? or return enum_for(__method__) { size }
  # Instead of directly using @hash.delete_if, perform enumeration
  # using self.each that subclasses may override.
  select(&block).each { |o| @hash.delete(o) }
  self
end

difference (enum)

Alias for: -

disjoint? (set)

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

Set[1, 2, 3].disjoint? Set[3, 4]   #=> false
Set[1, 2, 3].disjoint? Set[4, 5]   #=> true
Set[1, 2, 3].disjoint? [3, 4]      #=> false
Set[1, 2, 3].disjoint? 4..5        #=> true

# File lib/set.rb, line 492
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).

require 'set'
numbers = Set[1, 3, 4, 6, 9, 10, 11]
set = numbers.divide { |i,j| (i - j).abs == 1 }
set        #=> #<Set: {#<Set: {1}>,
           #           #<Set: {11, 9, 10}>,
           #           #<Set: {3, 4}>,
           #           #<Set: {6}>}>

Returns an enumerator if no block is given.

# File lib/set.rb, line 771
def divide(&func)
  func or return enum_for(__method__) { size }

  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 499
def each(&block)
  block_given? 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 307
def empty?
  @hash.empty?
end

filter! (&block)

Equivalent to Set#select!

Alias for: select!

flatten ()

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

# File lib/set.rb, line 377
def flatten
  self.class.new.flatten_merge(self)
end

flatten! ()

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

# File lib/set.rb, line 383
def flatten!
  replace(flatten()) if any?(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?

# File lib/set.rb, line 393
def include?(o)
  @hash[o]
end

Also aliased as: member?, ===

initialize_clone (orig, **options)

Clone internal hash.

Calls superclass method

# File lib/set.rb, line 290
def initialize_clone(orig, **options)
  super
  @hash = orig.instance_variable_get(:@hash).clone(**options)
end

initialize_dup (orig)

Dup internal hash.

Calls superclass method

# File lib/set.rb, line 284
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 811
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

Also aliased as: to_s

intersect? (set)

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

Set[1, 2, 3].intersect? Set[4, 5]   #=> false
Set[1, 2, 3].intersect? Set[3, 4]   #=> true
Set[1, 2, 3].intersect? 4..5        #=> false
Set[1, 2, 3].intersect? [3, 4]      #=> true

# File lib/set.rb, line 470
def intersect?(set)
  case set
  when Set
    if size < set.size
      any?(set)
    else
      set.any?(self)
    end
  when Enumerable
    set.any?(self)
  else
    raise ArgumentError, "value must be enumerable"
  end
end

intersection (enum)

Alias for: &

join (separator=nil)

Returns a string created by converting each element of the set to a string See also: Array#join

# File lib/set.rb, line 803
def join(separator=nil)
  to_a.join(separator)
end

keep_if (&block)

Deletes every element of the set for which block evaluates to false, and returns self. Returns an enumerator if no block is given.

# File lib/set.rb, line 554
def keep_if(&block)
  block_given? or return enum_for(__method__) { size }
  # Instead of directly using @hash.keep_if, perform enumeration
  # using self.each that subclasses may override.
  reject(&block).each { |o| @hash.delete(o) }
  self
end

length ()

Alias for: size

map! ()

Alias for: collect!

member? (o)

Alias for: include?

merge (*enums, **nil)

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

# File lib/set.rb, line 595
def merge(*enums, **nil)
  enums.each do |enum|
    if enum.instance_of?(self.class)
      @hash.update(enum.instance_variable_get(:@hash))
    else
      do_with_enum(enum) { |o| add(o) }
    end
  end

  self
end

proper_subset? (set)

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

# File lib/set.rb, line 438
def proper_subset?(set)
  case
  when set.instance_of?(self.class) && @hash.respond_to?(:<)
    @hash < set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size < set.size && all?(set)
  else
    raise ArgumentError, "value must be a set"
  end
end

Also aliased as: <

proper_superset? (set)

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

# File lib/set.rb, line 412
def proper_superset?(set)
  case
  when set.instance_of?(self.class) && @hash.respond_to?(:>)
    @hash > set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size > set.size && set.all?(self)
  else
    raise ArgumentError, "value must be a set"
  end
end

Also aliased as: >

reject! (&block)

Equivalent to Set#delete_if, but returns nil if no changes were made. Returns an enumerator if no block is given.

# File lib/set.rb, line 574
def reject!(&block)
  block_given? or return enum_for(__method__) { size }
  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.

set = Set[1, 'c', :s]             #=> #<Set: {1, "c", :s}>
set.replace([1, 2])               #=> #<Set: {1, 2}>
set                               #=> #<Set: {1, 2}>

# File lib/set.rb, line 327
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

reset ()

Resets the internal state after modification to existing elements and returns self.

Elements will be reindexed and deduplicated.

# File lib/set.rb, line 699
def reset
  if @hash.respond_to?(:rehash)
    @hash.rehash # This should perform frozenness check.
  else
    raise FrozenError, "can't modify frozen #{self.class.name}" if frozen?
  end
  self
end

select! (&block)

Equivalent to Set#keep_if, but returns nil if no changes were made. Returns an enumerator if no block is given.

# File lib/set.rb, line 583
def select!(&block)
  block_given? or return enum_for(__method__) { size }
  n = size
  keep_if(&block)
  self if size != n
end

Also aliased as: filter!

size ()

Returns the number of elements.

# File lib/set.rb, line 301
def size
  @hash.size
end

Also aliased as: length

subset? (set)

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

# File lib/set.rb, line 425
def subset?(set)
  case
  when set.instance_of?(self.class) && @hash.respond_to?(:<=)
    @hash <= set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size <= set.size && all?(set)
  else
    raise ArgumentError, "value must be a set"
  end
end

Also aliased as: <=

subtract (enum)

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

# File lib/set.rb, line 609
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.

# File lib/set.rb, line 399
def superset?(set)
  case
  when set.instance_of?(self.class) && @hash.respond_to?(:>=)
    @hash >= set.instance_variable_get(:@hash)
  when set.is_a?(Set)
    size >= set.size && set.all?(self)
  else
    raise ArgumentError, "value must be a set"
  end
end

Also aliased as: >=

to_a ()

Returns an array containing all elements in the set.

Set[1, 2].to_a                    #=> [1, 2]
Set[1, 'c', :s].to_a              #=> [1, "c", :s]

# File lib/set.rb, line 342
def to_a
  @hash.keys
end

to_json (*args)

Returns a JSON string representing self:

require 'json/add/set'
puts Set.new(%w/foo bar baz/).to_json

Output:

{"json_class":"Set","a":["foo","bar","baz"]}

# File ext/json/lib/json/add/set.rb, line 44
def to_json(*args)
  as_json.to_json(*args)
end

to_s ()

Alias for: inspect

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 351
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.

Set[1, 2, 3] | Set[2, 4, 5]         #=> #<Set: {1, 2, 3, 4, 5}>
Set[1, 5, 'z'] | (1..6)             #=> #<Set: {1, 5, "z", 2, 3, 4, 6}>

# File lib/set.rb, line 619
def |(enum)
  dup.merge(enum)
end

Also aliased as: +, union