Class: Hamster::Set

Inherits:
Object
  • Object
show all
Includes:
Enumerable, Immutable
Defined in:
lib/hamster/set.rb

Overview

`Hamster::Set` is a collection of unordered values with no duplicates. Testing whether an object is present in the `Set` can be done in constant time. `Set` is also `Enumerable`, so you can iterate over the members of the set with #each, transform them with #map, filter them with #select, and so on. Some of the `Enumerable` methods are overridden to return Hamster collections.

Like the `Set` class in Ruby's standard library, which we will call RubySet, `Hamster::Set` defines equivalency of objects using `#hash` and `#eql?`. No two objects with the same `#hash` code, and which are also `#eql?`, can coexist in the same `Set`. If one is already in the `Set`, attempts to add another one will have no effect.

`Set`s have no natural ordering and cannot be compared using `#<=>`. However, they define #<, #>, #<=, and #>= as shorthand for #proper_subset?, #proper_superset?, #subset?, and #superset? respectively.

The basic set-theoretic operations #union, #intersection, #difference, and #exclusion work with any `Enumerable` object.

A `Set` can be created in either of the following ways:

Hamster::Set.new([1, 2, 3]) # any Enumerable can be used to initialize
Hamster::Set['A', 'B', 'C', 'D']

The latter 2 forms of initialization can be used with your own, custom subclasses of `Hamster::Set`.

Unlike RubySet, all methods which you might expect to “modify” a `Hamster::Set` actually return a new set and leave the existing one unchanged.

Examples:

set1 = Hamster::Set[1, 2] # => Hamster::Set[1, 2]
set2 = Hamster::Set[1, 2] # => Hamster::Set[1, 2]
set1 == set2              # => true
set3 = set1.add("foo")    # => Hamster::Set[1, 2, "foo"]
set3 - set2               # => Hamster::Set["foo"]
set3.subset?(set1)        # => false
set1.subset?(set3)        # => true

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Enumerable

#<=>, #compact, #each_index, #grep, #grep_v, #group_by, #inspect, #join, #partition, #pretty_print, #product, #reject, #sum

Methods included from Enumerable

#to_list

Methods included from Immutable

included

Constructor Details

#initialize(items = []) ⇒ Set

Returns a new instance of Set.


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# File 'lib/hamster/set.rb', line 79

def initialize(items=[])
  @trie = Trie.new(0)
  items.each { |item| @trie.put!(item, nil) }
end

Class Method Details

.[](*items) ⇒ Set

Create a new `Set` populated with the given items.

Returns:


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# File 'lib/hamster/set.rb', line 57

def [](*items)
  items.empty? ? empty : new(items)
end

.alloc(trie = EmptyTrie) ⇒ Set

“Raw” allocation of a new `Set`. Used internally to create a new instance quickly after obtaining a modified Trie.

Returns:


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# File 'lib/hamster/set.rb', line 74

def alloc(trie = EmptyTrie)
  allocate.tap { |s| s.instance_variable_set(:@trie, trie) }
end

.emptySet

Return an empty `Set`. If used on a subclass, returns an empty instance of that class.

Returns:


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# File 'lib/hamster/set.rb', line 65

def empty
  @empty ||= self.new
end

Instance Method Details

#add(item) ⇒ Set Also known as: <<

Return a new `Set` with `item` added. If `item` is already in the set, return `self`.

Examples:

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

Parameters:

  • item (Object)

    The object to add

Returns:


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# File 'lib/hamster/set.rb', line 106

def add(item)
  include?(item) ? self : self.class.alloc(@trie.put(item, nil))
end

#add?(item) ⇒ Set, false

If `item` is not a member of this `Set`, return a new `Set` with `item` added. Otherwise, return `false`.

Examples:

Hamster::Set[1, 2, 3].add?(4) # => Hamster::Set[1, 2, 4, 3]
Hamster::Set[1, 2, 3].add?(2) # => false

Parameters:

  • item (Object)

    The object to add

Returns:


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# File 'lib/hamster/set.rb', line 120

def add?(item)
  !include?(item) && add(item)
end

#clearSet

Return an empty `Set` instance, of the same class as this one. Useful if you have multiple subclasses of `Set` and want to treat them polymorphically.

Returns:


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# File 'lib/hamster/set.rb', line 505

def clear
  self.class.empty
end

#delete(item) ⇒ Set

Return a new `Set` with `item` removed. If `item` is not a member of the set, return `self`.

Examples:

Hamster::Set[1, 2, 3].delete(1)  # => Hamster::Set[2, 3]
Hamster::Set[1, 2, 3].delete(99) # => Hamster::Set[1, 2, 3]

Parameters:

  • item (Object)

    The object to remove

Returns:


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# File 'lib/hamster/set.rb', line 133

def delete(item)
  trie = @trie.delete(item)
  new_trie(trie)
end

#delete?(item) ⇒ Set, false

If `item` is a member of this `Set`, return a new `Set` with `item` removed. Otherwise, return `false`.

Examples:

Hamster::Set[1, 2, 3].delete?(1)  # => Hamster::Set[2, 3]
Hamster::Set[1, 2, 3].delete?(99) # => false

Parameters:

  • item (Object)

    The object to remove

Returns:


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# File 'lib/hamster/set.rb', line 147

def delete?(item)
  include?(item) && delete(item)
end

#difference(other) ⇒ Set Also known as: subtract, -

Return a new `Set` with all the items in `other` removed. `other` can be any `Enumerable` object.

Examples:

Hamster::Set[1, 2] - Hamster::Set[2, 3] # => Hamster::Set[1]

Parameters:

  • other (Enumerable)

    The collection to subtract from this set

Returns:


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# File 'lib/hamster/set.rb', line 347

def difference(other)
  trie = if (@trie.size <= other.size) && (other.is_a?(Hamster::Set) || (defined?(::Set) && other.is_a?(::Set)))
    @trie.select { |key, _| !other.include?(key) }
  else
    @trie.bulk_delete(other)
  end
  new_trie(trie)
end

#disjoint?(other) ⇒ Boolean

Return `true` if this `Set` and `other` do not share any items.

Examples:

Hamster::Set[1, 2].disjoint?(Hamster::Set[8, 9]) # => true

Parameters:

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 449

def disjoint?(other)
  if other.size <= size
    other.each { |item| return false if include?(item) }
  else
    # See comment on #subset?
    if other.size >= 150 && @trie.size >= 190 && !(other.is_a?(Hamster::Set) || other.is_a?(::Set))
      other = ::Set.new(other)
    end
    each { |item| return false if other.include?(item) }
  end
  true
end

#each {|item| ... } ⇒ self, Enumerator

Call the block once for each item in this `Set`. No specific iteration order is guaranteed, but the order will be stable for any particular `Set`. If no block is given, an `Enumerator` is returned instead.

Examples:

Hamster::Set["Dog", "Elephant", "Lion"].each { |e| puts e }
Elephant
Dog
Lion
# => Hamster::Set["Dog", "Elephant", "Lion"]

Yields:

  • (item)

    Once for each item.

Returns:

  • (self, Enumerator)

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# File 'lib/hamster/set.rb', line 164

def each
  return to_enum if not block_given?
  @trie.each { |key, _| yield(key) }
  self
end

#empty?Boolean

Return `true` if this `Set` contains no items.

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 86

def empty?
  @trie.empty?
end

#eql?(other) ⇒ Boolean Also known as: ==

Return true if `other` has the same type and contents as this `Set`.

Parameters:

  • other (Object)

    The object to compare with

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 513

def eql?(other)
  return true if other.equal?(self)
  return false if not instance_of?(other.class)
  other_trie = other.instance_variable_get(:@trie)
  return false if @trie.size != other_trie.size
  @trie.each do |key, _|
    return false if !other_trie.key?(key)
  end
  true
end

#exclusion(other) ⇒ Set Also known as: ^

Return a new `Set` which contains all the items which are members of this `Set` or of `other`, but not both. `other` can be any `Enumerable` object.

Examples:

Hamster::Set[1, 2] ^ Hamster::Set[2, 3] # => Hamster::Set[1, 3]

Parameters:

  • other (Enumerable)

    The collection to take the exclusive disjunction of

Returns:


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# File 'lib/hamster/set.rb', line 366

def exclusion(other)
  ((self | other) - (self & other))
end

#firstObject

Return a member of this `Set`. The member chosen will be the first one which would be yielded by #each. If the set is empty, return `nil`.

Examples:

Hamster::Set["A", "B", "C"].first # => "C"

Returns:

  • (Object)

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# File 'lib/hamster/set.rb', line 243

def first
  (entry = @trie.at(0)) && entry[0]
end

#flattenSet

Recursively insert the contents of any nested `Set`s into this `Set`, and remove them.

Examples:

Hamster::Set[Hamster::Set[1, 2], Hamster::Set[3, 4]].flatten
# => Hamster::Set[1, 2, 3, 4]

Returns:


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# File 'lib/hamster/set.rb', line 481

def flatten
  reduce(self.class.empty) do |set, item|
    next set.union(item.flatten) if item.is_a?(Set)
    set.add(item)
  end
end

#hashInteger

See `Object#hash`.

Returns:

  • (Integer)

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# File 'lib/hamster/set.rb', line 527

def hash
  reduce(0) { |hash, item| (hash << 5) - hash + item.hash }
end

#include?(object) ⇒ Boolean Also known as: member?

Return `true` if the given item is present in this `Set`. More precisely, return `true` if an object with the same `#hash` code, and which is also `#eql?` to the given object is present.

Examples:

Hamster::Set["A", "B", "C"].include?("B") # => true
Hamster::Set["A", "B", "C"].include?("Z") # => false

Parameters:

  • object (Object)

    The object to check for

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 231

def include?(object)
  @trie.key?(object)
end

#intersect?(other) ⇒ Boolean

Return `true` if this `Set` and `other` have at least one item in common.

Examples:

Hamster::Set[1, 2].intersect?(Hamster::Set[2, 3]) # => true

Parameters:

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 469

def intersect?(other)
  !disjoint?(other)
end

#intersection(other) ⇒ Set Also known as: &

Return a new `Set` which contains all the items which are members of both this `Set` and `other`. `other` can be any `Enumerable` object.

Examples:

Hamster::Set[1, 2] & Hamster::Set[2, 3] # => Hamster::Set[2]

Parameters:

  • other (Enumerable)

    The collection to intersect with

Returns:


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# File 'lib/hamster/set.rb', line 324

def intersection(other)
  if other.size < @trie.size
    if other.is_a?(Hamster::Set)
      trie = other.instance_variable_get(:@trie).select { |key, _| include?(key) }
    else
      trie = Trie.new(0)
      other.each { |obj| trie.put!(obj, nil) if include?(obj) }
    end
  else
    trie = @trie.select { |key, _| other.include?(key) }
  end
  new_trie(trie)
end

#map {|item| ... } ⇒ Set Also known as: collect

Call the block once for each item in this `Set`. All the values returned from the block will be gathered into a new `Set`. If no block is given, an `Enumerator` is returned instead.

Examples:

Hamster::Set["Cat", "Elephant", "Dog", "Lion"].map { |e| e.size }
# => Hamster::Set[8, 4, 3]

Yields:

  • (item)

    Once for each item.

Returns:


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# File 'lib/hamster/set.rb', line 214

def map
  return enum_for(:map) if not block_given?
  return self if empty?
  self.class.new(super)
end

#marshal_dumpObject


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# File 'lib/hamster/set.rb', line 542

def marshal_dump
  output = {}
  each do |key|
    output[key] = nil
  end
  output
end

#marshal_load(dictionary) ⇒ Object


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# File 'lib/hamster/set.rb', line 551

def marshal_load(dictionary)
  @trie = dictionary.reduce(EmptyTrie) do |trie, key_value|
    trie.put(key_value.first, nil)
  end
end

#proper_subset?(other) ⇒ Boolean Also known as: <

Returns `true` if `other` contains all the items in this `Set`, plus at least one item which is not in this set.

Examples:

Hamster::Set[2, 3].proper_subset?(Hamster::Set[1, 2, 3])    # => true
Hamster::Set[1, 2, 3].proper_subset?(Hamster::Set[1, 2, 3]) # => false

Parameters:

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 418

def proper_subset?(other)
  return false if other.size <= size
  # See comments above
  if other.size >= 150 && @trie.size >= 190 && !(other.is_a?(Hamster::Set) || other.is_a?(::Set))
    other = ::Set.new(other)
  end
  all? { |item| other.include?(item) }
end

#proper_superset?(other) ⇒ Boolean Also known as: >

Returns `true` if this `Set` contains all the items in `other`, plus at least one item which is not in `other`.

Examples:

Hamster::Set[1, 2, 3].proper_superset?(Hamster::Set[2, 3])    # => true
Hamster::Set[1, 2, 3].proper_superset?(Hamster::Set[1, 2, 3]) # => false

Parameters:

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 437

def proper_superset?(other)
  other.proper_subset?(self)
end

#reverse_each {|item| ... } ⇒ self

Call the block once for each item in this `Set`. Iteration order will be the opposite of #each. If no block is given, an `Enumerator` is returned instead.

Examples:

Hamster::Set["Dog", "Elephant", "Lion"].reverse_each { |e| puts e }
Lion
Dog
Elephant
# => Hamster::Set["Dog", "Elephant", "Lion"]

Yields:

  • (item)

    Once for each item.

Returns:

  • (self)

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# File 'lib/hamster/set.rb', line 183

def reverse_each
  return enum_for(:reverse_each) if not block_given?
  @trie.reverse_each { |key, _| yield(key) }
  self
end

#sampleObject

Return a randomly chosen item from this `Set`. If the set is empty, return `nil`.

Examples:

Hamster::Set[1, 2, 3, 4, 5].sample # => 3

Returns:

  • (Object)

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# File 'lib/hamster/set.rb', line 497

def sample
  empty? ? nil : @trie.at(rand(size))[0]
end

#select {|item| ... } ⇒ Set Also known as: find_all, keep_if

Return a new `Set` with all the items for which the block returns true.

Examples:

Hamster::Set["Elephant", "Dog", "Lion"].select { |e| e.size >= 4 }
# => Hamster::Set["Elephant", "Lion"]

Yields:

  • (item)

    Once for each item.

Returns:


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# File 'lib/hamster/set.rb', line 196

def select
  return enum_for(:select) unless block_given?
  trie = @trie.select { |key, _| yield(key) }
  new_trie(trie)
end

#sizeInteger Also known as: length

Return the number of items in this `Set`.

Returns:

  • (Integer)

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# File 'lib/hamster/set.rb', line 92

def size
  @trie.size
end

#sort {|a, b| ... } ⇒ SortedSet

Return a Hamster::SortedSet which contains the same items as this `Set`, ordered by the given comparator block.

Examples:

Hamster::Set["Elephant", "Dog", "Lion"].sort
# => Hamster::SortedSet["Dog", "Elephant", "Lion"]
Hamster::Set["Elephant", "Dog", "Lion"].sort { |a,b| a.size <=> b.size }
# => Hamster::SortedSet["Dog", "Lion", "Elephant"]

Yields:

  • (a, b)

    Any number of times with different pairs of elements.

Yield Returns:

  • (Integer)

    Negative if the first element should be sorted lower, positive if the latter element, or 0 if equal.

Returns:


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# File 'lib/hamster/set.rb', line 261

def sort(&comparator)
  SortedSet.new(self.to_a, &comparator)
end

#sort_by {|item| ... } ⇒ SortedSet

Return a Hamster::SortedSet which contains the same items as this `Set`, ordered by mapping each item through the provided block to obtain sort keys, and then sorting the keys.

Examples:

Hamster::Set["Elephant", "Dog", "Lion"].sort_by { |e| e.size }
# => Hamster::SortedSet["Dog", "Lion", "Elephant"]

Yields:

  • (item)

    Once for each item to create the set, and then potentially again depending on what operations are performed on the returned Hamster::SortedSet. As such, it is recommended that the block be a pure function.

Yield Returns:

  • (Object)

    sort key for the item

Returns:


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# File 'lib/hamster/set.rb', line 279

def sort_by(&mapper)
  SortedSet.new(self.to_a, &mapper)
end

#subset?(other) ⇒ Boolean Also known as: <=

Return `true` if all items in this `Set` are also in `other`.

Examples:

Hamster::Set[2, 3].subset?(Hamster::Set[1, 2, 3]) # => true

Parameters:

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 378

def subset?(other)
  return false if other.size < size

  # This method has the potential to be very slow if 'other' is a large Array, so to avoid that,
  #   we convert those Arrays to Sets before checking presence of items
  # Time to convert Array -> Set is linear in array.size
  # Time to check for presence of all items in an Array is proportional to set.size * array.size
  # Note that both sides of that equation have array.size -- hence those terms cancel out,
  #   and the break-even point is solely dependent on the size of this collection
  # After doing some benchmarking to estimate the constants, it appears break-even is at ~190 items
  # We also check other.size, to avoid the more expensive #is_a? checks in cases where it doesn't matter
  #
  if other.size >= 150 && @trie.size >= 190 && !(other.is_a?(Hamster::Set) || other.is_a?(::Set))
    other = ::Set.new(other)
  end
  all? { |item| other.include?(item) }
end

#superset?(other) ⇒ Boolean Also known as: >=

Return `true` if all items in `other` are also in this `Set`.

Examples:

Hamster::Set[1, 2, 3].superset?(Hamster::Set[2, 3]) # => true

Parameters:

Returns:

  • (Boolean)

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# File 'lib/hamster/set.rb', line 404

def superset?(other)
  other.subset?(self)
end

#to_setself

Return `self`.

Returns:

  • (self)

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# File 'lib/hamster/set.rb', line 537

def to_set
  self
end

#union(other) ⇒ Set Also known as: |, +, merge

Return a new `Set` which contains all the members of both this `Set` and `other`. `other` can be any `Enumerable` object.

Examples:

Hamster::Set[1, 2] | Hamster::Set[2, 3] # => Hamster::Set[1, 2, 3]

Parameters:

  • other (Enumerable)

    The collection to merge with

Returns:


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# File 'lib/hamster/set.rb', line 291

def union(other)
  if other.is_a?(Hamster::Set)
    if other.size > size
      small_set_pairs = @trie
      large_set_trie = other.instance_variable_get(:@trie)
    else
      small_set_pairs = other.instance_variable_get(:@trie)
      large_set_trie = @trie
    end
  else
    if other.respond_to?(:lazy)
      small_set_pairs = other.lazy.map { |e| [e, nil] }
    else
      small_set_pairs = other.map { |e| [e, nil] }
    end
    large_set_trie = @trie
  end

  trie = large_set_trie.bulk_put(small_set_pairs)
  new_trie(trie)
end