yaml_equalizer.rb

def array_wrap(obj)
  case obj
  when Array then obj.map(&method(:array_wrap_hash_values))
  when Hash  then array_wrap([obj])
  else            obj
  end
end

def array_wrap_hash_values(obj)
  case obj
  when Hash then obj.transform_values(&method(:array_wrap))
  else           obj
  end
end

maybewithout = {eins: 1, zwei: 2, drei: {vier: 3, fünf: 4}}
with = array_wrap(maybewithout)

pp with # should show "[eins: 1, zwei: 2, drei: [{vier: 3, fünf: 4}]]"