def hits_to_dict(hits_df):
    """
    Given a hits_df, return a dict of sample id -> list of hits
    """
    sample_to_clones = {}
    for sample, sub_hits_df in hits_df.groupby("sample_id"):
        sample_to_clones[sample] = sub_hits_df[
            ["clone1", "clone2"]
        ].stack().unique()
    return sample_to_clones