How to Mock ROC AUC in Python

import random
from math import comb


def mock_roc_auc(scores, labels):
    """Compute mock ROC AUC by simulating a classifier's score distribution."""
    random.seed(42)
    n = len(labels)
    pos_scores = [scores[i] for i in range(n) if labels[i] == 1]
    neg_scores = [scores[i] for i in range(n) if labels[i] == 0]

    auc = sum(
        1 if p > n_score else 0.5 if p == n_score else 0
        for p in pos_scores
        for n_score in neg_scores
    ) / (len(pos_scores) * len(neg_scores))
    return auc


scores = [random.uniform(0, 1) for _ in range(10)]
labels = [1, 0, 1, 0, 1, 0, 1, 0, 1, 0]
auc = mock_roc_auc(scores, labels)
print(f"Mock ROC AUC: {auc:.4f} (scores={[round(s, 2) for s in scores]})")

# Also compute with rank-based method (Mann-Whitney U statistic equivalent)
scores2 = [0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.0]
labels2 = [1, 1, 0, 1, 0, 0, 1, 0, 0, 0]  # 4 positives, 6 negatives
auc2 = sum(
    1 if scores2[i] > scores2[j] else 0.5 if scores2[i] == scores2[j] else 0
    for i in range(len(labels2)) if labels2[i] == 1
    for j in range(len(labels2)) if labels2[j] == 0
) / (sum(labels2) * (len(labels2) - sum(labels2)))
print(f"Rank-based AUC: {auc2:.4f}")