Contents

class Array

  # Yields the block to each unique combination of _n_ elements.
  #
  #   a = %w|a b c d|
  #   a.each_combination(3) do |c|
  #     p c
  #   end
  #
  # produces
  #
  #   ["a", "b", "c"]
  #   ["a", "b", "d"]
  #   ["a", "c", "d"]
  #   ["b", "c", "d"]
  #
  def each_combination(k=2)
    n = self.size 
    return unless (1..n) === k
    idx = (0...k).to_a
    loop do
      yield self.values_at(*idx)
      i = k - 1
      i -= 1 while idx[i] == n - k + i
      break if i < 0
      idx[i] += 1
      (i + 1 ... k).each {|j| idx[j] = idx[i] + j - i}
    end
  end

end


#__TEST__

if $0 == __FILE__
  require 'test/unit'
  
  class TestCase < Test::Unit::TestCase
    a = [1, 2, 1]
    z = []
    a.each_combination(2) { |c| z << c }
    assert_equal([[1,2],[1,1],[1,1],[2,1]], z)
  end
end

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
facets-0.7.0	lib/facet/array/each_combination.rb
facets-0.7.1	lib/facet/array/each_combination.rb