Permutations of a hash of arrays

hash_of_arrays_permutations.rb

# Input: 
# choices = {
#   'color' => %w(blue red green),
#   'sizes' => %w(small medium large extra-large),
#   'style' => %w(tshirt longsleeve)
# }
# 
# Output:
# [{"sizes"=>"small", "color"=>"blue", "style"=>"tshirt"},
#  {"sizes"=>"small", "color"=>"blue", "style"=>"longsleeve"},
#  {"sizes"=>"medium", "color"=>"blue", "style"=>"tshirt"},
#  {"sizes"=>"medium", "color"=>"blue", "style"=>"longsleeve"},
#  {"sizes"=>"large", "color"=>"blue", "style"=>"tshirt"},
#  {"sizes"=>"large", "color"=>"blue", "style"=>"longsleeve"},
#  {"sizes"=>"extra-large", "color"=>"blue", "style"=>"tshirt"},
#  {"sizes"=>"extra-large", "color"=>"blue", "style"=>"longsleeve"},
#  {"sizes"=>"small", "color"=>"red", "style"=>"tshirt"},
#  {"sizes"=>"small", "color"=>"red", "style"=>"longsleeve"},
#  {"sizes"=>"medium", "color"=>"red", "style"=>"tshirt"},
#  {"sizes"=>"medium", "color"=>"red", "style"=>"longsleeve"},
#  {"sizes"=>"large", "color"=>"red", "style"=>"tshirt"},
#  {"sizes"=>"large", "color"=>"red", "style"=>"longsleeve"},
#  {"sizes"=>"extra-large", "color"=>"red", "style"=>"tshirt"},
#  {"sizes"=>"extra-large", "color"=>"red", "style"=>"longsleeve"},
#  {"sizes"=>"small", "color"=>"green", "style"=>"tshirt"},
#  {"sizes"=>"small", "color"=>"green", "style"=>"longsleeve"},
#  {"sizes"=>"medium", "color"=>"green", "style"=>"tshirt"},
#  {"sizes"=>"medium", "color"=>"green", "style"=>"longsleeve"},
#  {"sizes"=>"large", "color"=>"green", "style"=>"tshirt"},
#  {"sizes"=>"large", "color"=>"green", "style"=>"longsleeve"},
#  {"sizes"=>"extra-large", "color"=>"green", "style"=>"tshirt"},
#  {"sizes"=>"extra-large", "color"=>"green", "style"=>"longsleeve"}]

class Hash
  def permutations_of_arrays
    recursive_permute_arrays([], 0, {}, sort, count)
  end

  private
  def recursive_permute_arrays(acc, choices_index, chosen, self_sort, self_count)
    key, values = self_sort[choices_index]
    values.each do |val|
      chosen[key] = val
      if choices_index + 1 < self_count
        acc = recursive_permute_arrays(acc, choices_index + 1, chosen, self_sort, self_count)
      else
        acc << chosen.dup
      end
    end
    acc
  end
end