def make_network_undirected(n_df):
    """
    Make the network undirected; that is, the network should be symmetric, but
    only the edges in one direction are included.  So make the edges in the
    other direction explicit in the network. This assumes that the first two
    columns are the two nodes.

    Parameters:
        n_df (list): the data

    Returns:
        list: the modified data
    """

    return n_df + [[n[1], n[0]] + n[2:] for n in n_df]