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Set

This library provides the Set class, which deals with 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 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 #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

What's Here

First, what's elsewhere. Class Set:

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:

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 - Adds each given 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.

Public Class Methods

[](*ary) click to toggle source

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 set.rb, line 229
def self.[](*ary)
  new(ary)
end
            
new(enum = nil) click to toggle source

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 set.rb, line 244
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) click to toggle source

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 set.rb, line 647
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) click to toggle source
Alias for: |
-(enum) click to toggle source

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 set.rb, line 637
def -(enum)
  dup.subtract(enum)
end
            
Also aliased as: difference
<(set) click to toggle source
Alias for: proper_subset?
<<(o) click to toggle source
Alias for: add
<=(set) click to toggle source
Alias for: subset?
<=>(set) click to toggle source

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 set.rb, line 462
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) click to toggle source

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 set.rb, line 681
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) click to toggle source

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) click to toggle source
Alias for: proper_superset?
>=(set) click to toggle source
Alias for: superset?
^(enum) click to toggle source

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 set.rb, line 668
def ^(enum)
  n = Set.new(enum)
  each { |o| n.add(o) unless n.delete?(o) }
  n
end
            
add(o) click to toggle source

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 set.rb, line 520
def add(o)
  @hash[o] = true
  self
end
            
Also aliased as: <<
add?(o) click to toggle source

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 set.rb, line 532
def add?(o)
  add(o) unless include?(o)
end
            
classify() click to toggle source

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 set.rb, line 750
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() click to toggle source

Removes all elements and returns self.

set = Set[1, 'c', :s]             #=> #<Set: {1, "c", :s}>
set.clear                         #=> #<Set: {}>
set                               #=> #<Set: {}>
 
               # File set.rb, line 325
def clear
  @hash.clear
  self
end
            
collect!() click to toggle source

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

 
               # File set.rb, line 573
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() click to toggle source

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

 
               # File set.rb, line 258
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?() click to toggle source

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

 
               # File set.rb, line 269
def compare_by_identity?
  @hash.respond_to?(:compare_by_identity?) && @hash.compare_by_identity?
end
            
delete(o) click to toggle source

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

 
               # File set.rb, line 538
def delete(o)
  @hash.delete(o)
  self
end
            
delete?(o) click to toggle source

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

 
               # File set.rb, line 545
def delete?(o)
  delete(o) if include?(o)
end
            
delete_if() click to toggle source

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

 
               # File set.rb, line 552
def delete_if
  block_given? or return enum_for(__method__) { size }
  # @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) click to toggle source
Alias for: -
disjoint?(set) click to toggle source

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 set.rb, line 501
def disjoint?(set)
  !intersect?(set)
end
            
divide(&func) click to toggle source

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 set.rb, line 778
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) click to toggle source

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 set.rb, line 508
def each(&block)
  block or return enum_for(__method__) { size }
  @hash.each_key(&block)
  self
end
            
empty?() click to toggle source

Returns true if the set contains no elements.

 
               # File set.rb, line 316
def empty?
  @hash.empty?
end
            
filter!(&block) click to toggle source

Equivalent to #select!

Alias for: select!
flatten() click to toggle source

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

 
               # File set.rb, line 386
def flatten
  self.class.new.flatten_merge(self)
end
            
flatten!() click to toggle source

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

 
               # File set.rb, line 392
def flatten!
  replace(flatten()) if any? { |e| e.is_a?(Set) }
end
            
include?(o) click to toggle source

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 set.rb, line 402
def include?(o)
  @hash[o]
end
            
Also aliased as: member?, ===
initialize_clone(orig, **options) click to toggle source

Clone internal hash.

 
               # File set.rb, line 292
def initialize_clone(orig, **options)
  super
  @hash = orig.instance_variable_get(:@hash).clone(**options)
end
            
initialize_dup(orig) click to toggle source

Dup internal hash.

 
               # File set.rb, line 285
def initialize_dup(orig)
  super
  @hash = orig.instance_variable_get(:@hash).dup
end
            
inspect() click to toggle source

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

 
               # File set.rb, line 818
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) click to toggle source

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 set.rb, line 479
def intersect?(set)
  case set
  when Set
    if size < set.size
      any? { |o| set.include?(o) }
    else
      set.any? { |o| include?(o) }
    end
  when Enumerable
    set.any? { |o| include?(o) }
  else
    raise ArgumentError, "value must be enumerable"
  end
end
            
intersection(enum) click to toggle source
Alias for: &
join(separator=nil) click to toggle source

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

 
               # File set.rb, line 810
def join(separator=nil)
  to_a.join(separator)
end
            
keep_if() click to toggle source

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

 
               # File set.rb, line 563
def keep_if
  block_given? or return enum_for(__method__) { size }
  # @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() click to toggle source
Alias for: size
map!() click to toggle source
Alias for: collect!
member?(o) click to toggle source
Alias for: include?
merge(enum) click to toggle source

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

 
               # File set.rb, line 604
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) click to toggle source

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

 
               # File set.rb, line 447
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? { |o| set.include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
            
Also aliased as: <
proper_superset?(set) click to toggle source

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

 
               # File set.rb, line 421
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? { |o| include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
            
Also aliased as: >
reject!(&block) click to toggle source

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

 
               # File set.rb, line 583
def reject!(&block)
  block or return enum_for(__method__) { size }
  n = size
  delete_if(&block)
  self if size != n
end
            
replace(enum) click to toggle source

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 set.rb, line 336
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() click to toggle source

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

Elements will be reindexed and deduplicated.

 
               # File set.rb, line 706
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) click to toggle source

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

 
               # File set.rb, line 592
def select!(&block)
  block or return enum_for(__method__) { size }
  n = size
  keep_if(&block)
  self if size != n
end
            
Also aliased as: filter!
size() click to toggle source

Returns the number of elements.

 
               # File set.rb, line 310
def size
  @hash.size
end
            
Also aliased as: length
subset?(set) click to toggle source

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

 
               # File set.rb, line 434
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? { |o| set.include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
            
Also aliased as: <=
subtract(enum) click to toggle source

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

 
               # File set.rb, line 616
def subtract(enum)
  do_with_enum(enum) { |o| delete(o) }
  self
end
            
superset?(set) click to toggle source

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

 
               # File set.rb, line 408
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? { |o| include?(o) }
  else
    raise ArgumentError, "value must be a set"
  end
end
            
Also aliased as: >=
to_a() click to toggle source

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

Set[1, 2].to_a                    #=> [1, 2]
Set[1, 'c', :s].to_a              #=> [1, "c", :s]
 
               # File set.rb, line 351
def to_a
  @hash.keys
end
            
to_s() click to toggle source
Alias for: inspect
to_set(klass = Set, *args, &block) click to toggle source

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 set.rb, line 360
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) click to toggle source
Alias for: |
|(enum) click to toggle source

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 set.rb, line 626
def |(enum)
  dup.merge(enum)
end
            
Also aliased as: +, union