hsh.rename_keys

class Hash
  # Accept a hash of values, changes the value in self
  # from the key in the param to be indexed at the value of param
  # and returns the new hash. Does not modify self.
  #
  # >> a = {"dog" => "meow", "bird" => "tweet" }
  # => {"bird"=>"tweet", "dog"=>"meow"}
  # >> a.rename_keys "dog" => "cat"
  # => {"cat"=>"meow", "bird"=>"tweet"}
  # >> a
  # => {"bird"=>"tweet", "dog"=>"meow"}
  def rename_keys(list)
    a = dup
    list.each_pair do |from, to|
      a[to] = a.delete(from)
    end
    a
  end
  
  # Same as hsh.rename_keys except it operates directly on self
  def rename_keys!(list)
    list.each_pair do |from, to|
      self[to] = self.delete(from)
    end
    self
  end
end