A plugin to allow union of arrays with Jekyll.

union.rb

module Jekyll
	module UnionFilter
		def union(input, array)
			unless array.respond_to?(:to_ary)
				array = Array.new
			end
			InputIterator.new(input).concat(array).uniq
		end
		
		class InputIterator
			include Enumerable

			def initialize(input)
				@input = if input.is_a?(Array)
					input.flatten
				elsif input.is_a?(Hash)
					[input]
				elsif input.is_a?(Enumerable)
					input
				else
					Array(input)
				end
			end

			def concat(args)
				to_a.concat(args)
			end

			def each
				@input.each do |e|
					yield(e.respond_to?(:to_liquid) ? e.to_liquid : e)
				end
			end
		end
	end
end

Liquid::Template.register_filter(Jekyll::UnionFilter)