Simplistic backport of Enumerable#slice_before from Ruby 1.9 to Ruby 1.8.

gistfile1.rb

class Array
  def slice_before
    [].tap do |chunks|
      each do |item|
        chunks << [] if yield(item) || chunks.empty?
        chunks.last << item
        chunks
      end
    end
  end
end

Here's the documentation.