Multiset library for Ruby

[Japanese]

Ruby implementation of multiset. Unlike ordinary set(see Ruby documentation for "set" library), multiset can store two or more same items.

Set[:a,:b,:c,:b,:b,:c] # => #<Set: {:b, :c, :a}>
Multiset[:a,:b,:c,:b,:b,:c] # => #<Multiset:#3 :b, #2 :c, #1 :a>

Multisets are typically used for counting elements and their numbers of appearances in collections.

# Counting the appearances of characters in a string
# (Ruby 1.8.7 or later)
Multiset.new("abracadabra".each_char)
# => #<Multiset:#5 "a", #2 "b", #2 "r", #1 "c", #1 "d">

# The same
m = Multiset.new
"abracadabra".each_char do |c| # replace with 'each_byte' in Ruby 1.8.6 or before
  m << c
end
p m
# => #<Multiset:#5 "a", #2 "b", #2 "r", #1 "c", #1 "d">

# The same but works with Ruby 1.8.6 or before
Multiset.new("abracadabra".split(//))
# => #<Multiset:#5 "a", #2 "b", #2 "r", #1 "c", #1 "d">

Modified Specifications

• From version 0.5.0, Multiset#sample returns nil if the multiset is empty, the same as Array#sample. (It was undefined before.).
• In version 0.4.0, many specifications are modified with compatibility lost:
  • Multiset.parse_string is abolished. (to fit to Ruby 1.9)
  • Multiset#map, Multiset#select, and so on now gives the same item to the given block only once. For example, Multiset[:a, :a, :a, :b].map{ … } calls the block for only twice, which is 4 times in the old behavior.
  • Multiset#map, Multiset#select, and so on now returns a Multiset rather than an Array.
  • Multiset#group_by now returns a Multimap rather than a Hash.
• From version 0.201, Multiset#classify and Multiset#classify_with returns an instance of Multimap.
• From version 0.12, methods Multiset#map, Multiset#map_with, and so on are added. Be careful that new Multiset#map is NOT equal to conventional Multiset#map(=Enumerable#map)!!

Other Major Updates

• From version 0.13, installation with setup.rb is avaliable. From 0.3.0, installation with Rubygems is available.
• From version 0.20, multimap is implemented.
• I found my mistake that I did not attach the text of GNU LGPL for setup.rb . The text is attached from version 0.132 and 0.202.

Install/Download

The library is available via Rubygems. Use the command

gem install multiset

.gem file is available at http://rubygems.org/gems/multiset.

Source codes are available at http://github.com/maraigue/multiset. You can fork or propose fixes on the library via Git.

[Old versions]

• Version 0.132(2008/3/2) [Download(tar.gz archive)]
• Version 0.202(2008/3/25) [Download(tar.gz archive)]

*This program is distributed under MIT License (0.3.* or after) / BSD license (0.2.* or before).

Document

Ver. 0.5.* (almost the same for version 0.4.*) Ver. 0.2.* Ver. 0.132

[Reverse reference] (Added on 2008/3/1)

Contact

email to main(at-mark)hhiro.net .

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