add Enumerable.all_combinations

lib/enumerable.rb

@@ -1,5 +1,22 @@
 module Enumerable
 
+  def self.all_combinations source
+    result_count = source.map(&:size).inject(:*)
+    group_count = 1
+    result = []
+    source.each do |elems|
+      row = []
+      group_count.times do
+        elems.each do |elem|
+          (result_count / group_count / elems.size).times { row << elem }
+        end
+      end
+      group_count *= elems.size
+      result << row
+    end
+    result.transpose
+  end
+
   def pairs
     return combination 2 if respond_to? :combination
     Enumerator.new do |yielder|

spec/enumerable_spec.rb

@@ -11,4 +11,10 @@
     array.pairs
   end
 
+  it 'should have a method to get all possible combinations of the passed elements' do
+    source = [[:a,:b], [:c], [:d,:e,:f]]
+    Enumerable.all_combinations(source).should == [[:a,:c,:d], [:a,:c,:e], [:a,:c,:f],
+                                                   [:b,:c,:d], [:b,:c,:e], [:b,:c,:f]]
+  end
+
 end