如何从tensorflow数据集数据集中获取字符串映射？

import tensorflow_datasets as tfds

dataset = tfds.load('dataset_name', split='train')

encoder = tfds.features.text.TokenTextEncoder.build_from_corpus(
    (data['text'].numpy() for data in dataset), target_vocab_size=2**13)

def encode(text_tensor, label):
    encoded_text = encoder.encode(text_tensor.numpy())
    return encoded_text, label

def encode_map_fn(text, label):
    encoded_text, label = tf.py_function(encode, inp=[text, label], Tout=(tf.int64, tf.int64))
    encoded_text.set_shape([None])
    label.set_shape([])
    return encoded_text, label

encoded_dataset = dataset.map(encode_map_fn)

decoder = tfds.features.text.TokenTextEncoder.build_from_corpus(
    (data['text'].numpy() for data in dataset), target_vocab_size=2**13)