# https://g...content-available-to-author-only...b.com/1481377
class Array
  def bunch(num)
    old = self.clone
    new = []
    while 1
      bunched = []
      num.times do
        bunched << old.shift
      end
      new << bunched
      break if old.empty?
    end
    new
  end
end

[1,2,3,5,6,7].keep_if {|i| i unless 0==i%2 }.bunch(2).each {|i| puts "#{i[0]}-#{i[1]}" }