def columns(seq_set, positions=None, feature=None, default=None,
            transpose=False):
    """
    Return a list of lists of elements at selected positions from all
    sequences of selected feature(s).

    Args:
        seq_set (SequenceSet): a sequence set.
        positions (list or int): list of positions in a sequence
           (default: None means all positions up to the length of the
           longest sequence are used)
        features (str or list): selected feature identifiers (default=None).
        default: the element to be used if sequence ends
            before the positions (the default default is None)
        transpose: whether to return the list of columns from sequences
            (default: False), or the list of sequences with selected
            columns only (True).

    Returns a list of list of elements at selected positions.

    The size of the returned list of list is |positions| x |features|.
    """

    return seq_set.columns(positions=positions, feature=feature,
                           default=default, transpose=transpose)