Add mask_first_token method

            continue

    return df

def mask_first_token():

    df = STSB_Dataset('data/stsbenchmark/sts-test.csv').as_dataframe

    i = -1

    for sent1 in sentences1_nlp:

        i += 1

        first_token = [token.text for token in sent1][0]

        df.iloc[i, 0] = df.iloc[i, 0].replace(first_token, get_random_string(random.randrange(1, 9)))

    i = -1

    for sent2 in sentences2_nlp:

        i += 1

        first_token = [token.text for token in sent1][0]

        df.iloc[i, 0] = df.iloc[i, 0].replace(first_token, get_random_string(random.randrange(1, 9)))

    return df