Takes a subset of columns

def take_column(self, keys, *extra_keys):
        """ Takes a subset of columns """
        import utool as ut
        keys = ut.ensure_iterable(keys) + list(extra_keys)
        key_to_list = ut.dict_subset(self._key_to_list, keys)
        newself = self.__class__(key_to_list, self._meta.copy())
        return newself