Add the enumerable module as a standalone file

git-svn-id: file:///home/svn/framework3/trunk@6415 4d416f70-5f16-0410-b530-b9f4589650da

lib/enumerable.rb

@@ -0,0 +1,115 @@
+#
+# This Module was developed by Thomas Hafner.
+# No other references about the author.
+#
+
+# TITLE:
+#
+#   Cartesian
+#
+# SUMMARY:
+#
+#   Cartesian product and similar methods.
+#
+# AUTHORS:
+#
+#   - Thomas Hafner
+
+#
+module Enumerable
+
+	class << self
+		# Provides the cross-product of two or more Enumerables.
+		# This is the class-level method. The instance method
+		# calls on this.
+		#
+		#   Enumerable.cart([1,2], [4], ["apple", "banana"])
+		#   #=> [[1, 4, "apple"], [1, 4, "banana"], [2, 4, "apple"], [2, 4, "banana"]]
+		#
+		#   Enumerable.cart([1,2], [3,4])
+		#   #=> [[1, 3], [1, 4], [2, 3], [2, 4]]
+
+		def cartesian_product(*enums, &block)
+			result = [[]]
+			while [] != enums
+				t, result = result, []
+				b, *enums = enums
+				t.each do |a|
+					b.each do |n|
+						result << a + [n]
+					end
+				end
+			end
+			if block_given?
+				result.each{ |e| block.call(e) }
+			else
+				result
+			end
+		end
+
+		alias_method :cart, :cartesian_product
+	end
+
+	# The instance level version of <tt>Enumerable::cartesian_product</tt>.	
+	#
+	#   a = []
+	#   [1,2].cart([4,5]){|elem| a << elem }
+	#   a  #=> [[1, 4],[1, 5],[2, 4],[2, 5]]
+
+	def cartesian_product(*enums, &block)
+		Enumerable.cartesian_product(self, *enums, &block)
+	end
+
+	alias :cart :cartesian_product
+
+	# Operator alias for cross-product.
+	#
+	#   a = [1,2] ** [4,5]
+	#   a  #=> [[1, 4],[1, 5],[2, 4],[2, 5]]
+	#
+	def **(enum)
+		Enumerable.cartesian_product(self, enum)
+	end
+
+	# Expected to be an enumeration of arrays. This method
+	# iterates through combinations of each in position.
+	#
+	#   a = [ [0,1], [2,3] ]
+	#   a.each_combo { |c| p c }
+	#
+	# produces
+	#
+	#   [0, 2]
+	#   [0, 3]
+	#   [1, 2]
+	#   [1, 3]
+	#
+	def each_combo
+		a = collect{ |x|
+			x.respond_to?(:to_a) ? x.to_a : 0..x
+		}
+
+		if a.size == 1
+			r = a.shift
+			r.each{ |n|
+				yield n
+			}
+		else
+			r = a.shift
+			r.each{ |n|
+				a.each_combo{ |s|
+					yield [n, *s]
+				}
+			}
+		end
+	end
+
+	# As with each_combo but returns combos collected in an array.
+	#
+	def combos
+		a = []
+		each_combo{ |c| a << c }
+		a
+	end
+
+end