Find every possible combination of a hash

every_combo.rb

class Hash
  def every_combo
    arr = self.to_a
    1.upto(arr.size).inject([]) do |memo, n|
      memo << arr.combination(n).to_a.map{|a| Hash[a] }
      memo
    end.flatten
  end
end

# Sample usage
#
# > {
#     :a => 1,
#     :b => 2,
#     :c => 3,
#     :d => 4,
#     :e => 5
#   }.every_combo
# 
# # => 
# [
#     [ 0] {
#         :a => 1
#     },
#     [ 1] {
#         :b => 2
#     },
#     [ 2] {
#         :c => 3
#     },
#     [ 3] {
#         :d => 4
#     },
#     [ 4] {
#         :e => 5
#     },
#     [ 5] {
#         :a => 1,
#         :b => 2
#     },
#     [ 6] {
#         :a => 1,
#         :c => 3
#     },
#     [ 7] {
#         :a => 1,
#         :d => 4
#     },
#     [ 8] {
#         :a => 1,
#         :e => 5
#     },
#     [ 9] {
#         :b => 2,
#         :c => 3
#     },
#     [10] {
#         :b => 2,
#         :d => 4
#     },
#     [11] {
#         :b => 2,
#         :e => 5
#     },
#     [12] {
#         :c => 3,
#         :d => 4
#     },
#     [13] {
#         :c => 3,
#         :e => 5
#     },
#     [14] {
#         :d => 4,
#         :e => 5
#     },
#     [15] {
#         :a => 1,
#         :b => 2,
#         :c => 3
#     },
#     [16] {
#         :a => 1,
#         :b => 2,
#         :d => 4
#     },
#     [17] {
#         :a => 1,
#         :b => 2,
#         :e => 5
#     },
#     [18] {
#         :a => 1,
#         :c => 3,
#         :d => 4
#     },
#     [19] {
#         :a => 1,
#         :c => 3,
#         :e => 5
#     },
#     [20] {
#         :a => 1,
#         :d => 4,
#         :e => 5
#     },
#     [21] {
#         :b => 2,
#         :c => 3,
#         :d => 4
#     },
#     [22] {
#         :b => 2,
#         :c => 3,
#         :e => 5
#     },
#     [23] {
#         :b => 2,
#         :d => 4,
#         :e => 5
#     },
#     [24] {
#         :c => 3,
#         :d => 4,
#         :e => 5
#     },
#     [25] {
#         :a => 1,
#         :b => 2,
#         :c => 3,
#         :d => 4
#     },
#     [26] {
#         :a => 1,
#         :b => 2,
#         :c => 3,
#         :e => 5
#     },
#     [27] {
#         :a => 1,
#         :b => 2,
#         :d => 4,
#         :e => 5
#     },
#     [28] {
#         :a => 1,
#         :c => 3,
#         :d => 4,
#         :e => 5
#     },
#     [29] {
#         :b => 2,
#         :c => 3,
#         :d => 4,
#         :e => 5
#     },
#     [30] {
#         :a => 1,
#         :b => 2,
#         :c => 3,
#         :d => 4,
#         :e => 5
#     }
# ]