some simple python utilities copied from other sources

find_best_f1_and_threshold.py

"""
Copied from sentence-transformers / sentence_transformers/evaluation/BinaryClassificationEvaluator.py
"""
def find_best_f1_and_threshold(scores, labels, high_score_more_similar: bool):
    assert len(scores) == len(labels)

    scores = np.asarray(scores)
    labels = np.asarray(labels)

    rows = list(zip(scores, labels))

    rows = sorted(rows, key=lambda x: x[0], reverse=high_score_more_similar)

    best_f1 = best_precision = best_recall = 0
    threshold = 0
    nextract = 0
    ncorrect = 0
    total_num_duplicates = sum(labels)

    for i in range(len(rows)-1):
        score, label = rows[i]
        nextract += 1

        if label == 1:
            ncorrect += 1

        if ncorrect > 0:
            precision = ncorrect / nextract
            recall = ncorrect / total_num_duplicates
            f1 = 2 * precision * recall / (precision + recall)
            if f1 > best_f1:
                best_f1 = f1
                best_precision = precision
                best_recall = recall
                threshold = (rows[i][0] + rows[i + 1][0]) / 2

    return best_f1, best_precision, best_recall, threshold