calculates ROC data points and returns roc_structure, a modified form of the score_structure format
    :param score_structure: list [(id, best_score, best_query, status, net decoy count, net active count), ..., ]
    :return auc_structure: list [(id, best_score, best_query, status, fpf, tpf), ..., ]

def make_auc_structure(score_structure):
    """
    calculates ROC data points and returns roc_structure, a modified form of the score_structure format
    :param score_structure: list [(id, best_score, best_query, status, net decoy count, net active count), ..., ]
    :return auc_structure: list [(id, best_score, best_query, status, fpf, tpf), ..., ]
    """

    n = len([x for x in score_structure if x[3] == '0'])   # Total no. of decoys
    p = len([x for x in score_structure if x[3] == '1'])   # Total no. of actives

    auc_structure = []

    for mol in score_structure:
        if n == 0:
            fpf = 0
        else:
            fpf = float(mol[4]) / n
        if p == 0:
            tpf = 0
        else:
            tpf = float(mol[5]) / p
        tup = mol[0:4] + (fpf, tpf)
        auc_structure.append(tup)

    return auc_structure