Combinatorics

• github.com/postmodern/combinatorics
• github.com/postmodern/combinatorics/issues
• Postmodern (postmodern.mod3 at gmail.com)

Description

A collection of modules and methods for performing Combinatoric calculations.

Features

• Adds powerset to Array and Set.
• Added Range#&, Range#upto and Range#downto.
• Adds Haskell/Python style list comprehensions via Array#comprehension.

Examples

Power-set of an Array:

require 'combinatorics/power_set'

[1,2,3,4].powerset
# => [[],
      [4],
      [3],
      [3, 4],
      [2],
      [2, 4],
      [2, 3],
      [2, 3, 4],
      [1],
      [1, 4],
      [1, 3],
      [1, 3, 4],
      [1, 2],
      [1, 2, 4],
      [1, 2, 3],
      [1, 2, 3, 4]]

Power-set of a Set:

Set['ab', 'cd', 'ef'].powerset
# => [#<Set: {}>,
      #<Set: {"ef"}>,
      #<Set: {"cd"}>,
      #<Set: {"cd", "ef"}>,
      #<Set: {"ab"}>,
      #<Set: {"ab", "ef"}>,
      #<Set: {"ab", "cd"}>,
      #<Set: {"ab", "cd", "ef"}>]

Find the intersecting sub-range between two ranges:

(1..50) & (20..100)
# => (20..50)

Enumerate over every sub-range between two ranges:

(1..5).upto(2..10).to_a
# => [1..5, 1..6, 1..7, 1..8, 1..9, 1..10,
      2..5, 2..6, 2..7, 2..8, 2..9, 2..10]

List comprehensions:

require 'combinatorics/list_comprehension'

[(0..10).step(2),('a'..'c')].comprehension.to_a
# => [[0, "a"],
      [0, "b"],
      [0, "c"],
      [2, "a"],
      [2, "b"],
      [2, "c"],
      [4, "a"],
      [4, "b"],
      [4, "c"],
      [6, "a"],
      [6, "b"],
      [6, "c"],
      [8, "a"],
      [8, "b"],
      [8, "c"],
      [10, "a"],
      [10, "b"],
      [10, "c"]]

Install

$ sudo gem install combinatorics

License

Copyright (c) 2010 Hal Brodigan

See LICENSE for license information.