A challenge set by sross. (See his Lisp solution: http://gist.github.com/79799)

gistfile1.rb

# Ensure that all the arrays in a hash are ordered the same (even if 
# they have missing elements).
def ordered?(hash_of_arrays)
  hash_of_arrays.all? do |k,v|
    hash_of_arrays.all? { |k2,v2| v - (v - v2) == v2 - (v2 - v) }
  end
end

ordered?({ 1 => [1, 2, 3, 4], 2 => [1, 3, 4], 3 => [2, 4, 5], 4 => [1, 2, 4, 6]})
#=> true

ordered?({ 1 => [1, 2, 3, 4], 2 => [1, 3, 4], 3 => [2, 4, 5], 4 => [1, 4, 2, 6]})
#=> false