CMRC Metric

# find longest common string
def find_lcs(s1, s2):
    m = [[0 for i in range(len(s2)+1)] for j in range(len(s1)+1)]
    mmax = 0
    p = 0
    for i in range(len(s1)):
        for j in range(len(s2)):
            if s1[i] == s2[j]:
                m[i+1][j+1] = m[i][j]+1
                if m[i+1][j+1] > mmax:
                    mmax=m[i+1][j+1]
                    p=i+1
    return s1[p-mmax:p], mmax


def calc_f1_score(answers, prediction):
    f1_scores = []
    for ans in answers:
        ans_segs = mixed_segmentation(ans, rm_punc=True)
        prediction_segs = mixed_segmentation(prediction, rm_punc=True)
        lcs, lcs_len = find_lcs(ans_segs, prediction_segs)
        if lcs_len == 0:
            f1_scores.append(0)
            continue
        precision   = 1.0 * lcs_len / len(prediction_segs)
        recall      = 1.0 * lcs_len / len(ans_segs)
        f1          = (2 * precision*recall) / (precision + recall)
        f1_scores.append(f1)
    return max(f1_scores)

# remove punctuation
def remove_punctuation(in_str):
    in_str = in_str.lower().strip()
    sp_char = ['-', ':', '_', '*', '^', '/', '\\', '~', '`', '+', '=', '，', '。', '：', '？', '！', '“', '”', '；', '’',
               '《', '》', '……', '·', '、', '「', '」', '（', '）', '－', '～', '『', '』']
    out_segs = []
    for char in in_str:
        if char in sp_char:
            continue
        else:
            out_segs.append(char)
    return ''.join(out_segs)


def calc_em_score(answers, prediction):
    em = 0
    for ans in answers:
        ans_ = remove_punctuation(ans)
        prediction_ = remove_punctuation(prediction)
        if ans_ == prediction_:
            em = 1
            break
    return em