test_ranking.py 文件源码

def _average_precision(y_true, y_score):
    """Alternative implementation to check for correctness of
    `average_precision_score`."""
    pos_label = np.unique(y_true)[1]
    n_pos = np.sum(y_true == pos_label)
    order = np.argsort(y_score)[::-1]
    y_score = y_score[order]
    y_true = y_true[order]

    score = 0
    for i in range(len(y_score)):
        if y_true[i] == pos_label:
            # Compute precision up to document i
            # i.e, percentage of relevant documents up to document i.
            prec = 0
            for j in range(0, i + 1):
                if y_true[j] == pos_label:
                    prec += 1.0
            prec /= (i + 1.0)
            score += prec

    return score / n_pos