Keras 训练在第二个 Epoch 后失败

Question

编辑这是生成器代码

def generate_batch(self, n_positive=50, negative_ratio=1.0, classification=False):
    # TODO: use `frequency` to reinforce positive labels
    # TODO: allow n_positive to use entire data set
    """
    Generate batches of samples for training

    :param n_positive: number of positive training examples
    :param negative_ratio: ratio of positive:negative training examples
    :param classification: determines type of loss function and network architecture
    :return: generator that products batches of training inputs/labels
    """


    pairs = self.index()
    batch_size = n_positive * (1 + negative_ratio)

    # Adjust label based on task
    if classification:
        neg_label = 0
    else:
        neg_label = -1

    # This creates a generator
    idx = 0 # TODO: make `max_recipe_length` config-driven once `structured_document` in Redshift is hstack'd
    while True:
        # batch = np.zeros((batch_size, 3))
        batch = []
        # randomly choose positive examples
        for idx, (recipe, document) in enumerate(random.sample(pairs, n_positive)):
            encoded = self.encode_pair(recipe, document)
            # TODO: refactor from append
            batch.append([encoded[0], encoded[1], 1])
            # logger.info('([encoded[0], encoded[1], 1]) %s', ([encoded[0], encoded[1], 1]))
            # batch[idx, :] = ([encoded[0], encoded[1], 1])

        # Increment idx by 1
        idx += 1

        # Add negative examples until reach batch size
        while idx < batch_size:
            # TODO: [?] optimize how negative sample inputs are constructed
            random_index_1, random_index_2 = random.randrange(len(self.ingredients_index)), \
                                             random.randrange(len(self.ingredients_index))
            random_recipe, random_document = self.pairs[random_index_1][0], self.pairs[random_index_2][1]

            # Check to make sure this is not a positive example
            if (random_recipe, random_document) not in self.pairs:
                # Add to batch and increment index
                encoded = self.encode_pair(random_recipe, random_document)
                # TODO: refactor from append
                batch.append([encoded[0], encoded[1], neg_label])
                # batch[idx, :] = ([encoded[0], encoded[1], neg_label])
                idx += 1

        # Make sure to shuffle order
        np.random.shuffle(batch)
        batch = np.array(batch)

        ingredients, documents, labels = np.array(batch[:, 0].tolist()), \
                                         np.array(batch[:, 1].tolist()), \
                                         np.array(batch[:, 2].tolist())


        yield {'ingredients': ingredients, 'documents': documents}, labels


batch = t.generate_batch(n_positive, negative_ratio=negative_ratio)
model = model(embedding_size, document_size, vocabulary_size=vocabulary_size)
h = model.fit_generator(
    batch,
    epochs=20,
    steps_per_epoch=int(training_size/(n_positive*(negative_ratio+1))),
    verbose=2
)

---

我有以下嵌入网络架构，它可以很好地学习我的小规模语料库（.fit_generator(...) 的形状错误

__________________________________________________________________________________________________
Layer (type)                    Output Shape         Param #     Connected to
==================================================================================================
ingredients (InputLayer)        (None, 46)           0
__________________________________________________________________________________________________
documents (InputLayer)          (None, 46)           0
__________________________________________________________________________________________________
ingredients_embedding (Embeddin (None, 46, 10)       100000      ingredients[0][0]
__________________________________________________________________________________________________
documents_embedding (Embedding) (None, 46, 10)       100000      documents[0][0]
__________________________________________________________________________________________________
lambda_1 (Lambda)               (None, 10)           0           ingredients_embedding[0][0]
__________________________________________________________________________________________________
lambda_2 (Lambda)               (None, 10)           0           documents_embedding[0][0]
__________________________________________________________________________________________________
dot_product (Dot)               (None, 1)            0           lambda_1[0][0]
                                                                 lambda_2[0][0]
__________________________________________________________________________________________________
reshape_1 (Reshape)             (None, 1)            0           dot_product[0][0]
==================================================================================================
Total params: 200,000
Trainable params: 200,000
Non-trainable params: 0

由以下模型代码生成：

def model(embedding_size, document_size, vocabulary_size=10000, classification=False):
    ingredients = Input(
        name='ingredients',
        shape=(document_size,)
    )
    documents = Input(
        name='documents',
        shape=(document_size,)
    )

    ingredients_embedding = Embedding(name='ingredients_embedding',
                                      input_dim=vocabulary_size,
                                      output_dim=embedding_size)(ingredients)

    document_embedding = Embedding(name='documents_embedding',
                                   input_dim=vocabulary_size,
                                   output_dim=embedding_size)(documents)

    # sum over the sentence dimension
    ingredients_embedding = Lambda(lambda x: K.sum(x, axis=-2))(ingredients_embedding)
    # sum over the sentence dimension
    document_embedding = Lambda(lambda x: K.sum(x, axis=-2))(document_embedding)

    merged = Dot(name='dot_product', normalize=True, axes=-1)([ingredients_embedding, document_embedding])

    merged = Reshape(target_shape=(1,))(merged)

    # If classification, add extra layer and loss function is binary cross entropy
    if classification:
        merged = Dense(1, activation='sigmoid')(merged)
        m = Model(inputs=[ingredients, documents], outputs=merged)
        m.compile(optimizer='Adam', loss='binary_crossentropy', metrics=['accuracy'])

    # Otherwise loss function is mean squared error
    else:
        m = Model(inputs=[ingredients, documents], outputs=merged)
        m.compile(optimizer='Adam', loss='mse')

    m.summary()

    save_model(m)
    return m

我可以在 10k 训练示例上训练此模型，但是当我将训练集大小增加到 100k 记录时，每次在第二个 epoch 之后都会出现以下错误。

Epoch 1/20
 - 8s - loss: 0.3181
Epoch 2/20
 - 6s - loss: 0.1086
Epoch 3/20
Traceback (most recent call last):
  File "run.py", line 38, in <module>
    verbose=2
  File "/usr/local/lib/python3.7/site-packages/keras/legacy/interfaces.py", line 91, in wrapper
    return func(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/keras/engine/training.py", line 1418, in fit_generator
    initial_epoch=initial_epoch)
  File "/usr/local/lib/python3.7/site-packages/keras/engine/training_generator.py", line 217, in fit_generator
    class_weight=class_weight)
  File "/usr/local/lib/python3.7/site-packages/keras/engine/training.py", line 1211, in train_on_batch
    class_weight=class_weight)
  File "/usr/local/lib/python3.7/site-packages/keras/engine/training.py", line 751, in _standardize_user_data
    exception_prefix='input')
  File "/usr/local/lib/python3.7/site-packages/keras/engine/training_utils.py", line 138, in standardize_input_data
    str(data_shape))
ValueError: Error when checking input: expected documents to have shape (46,) but got array with shape (1,)

Answer 1

问题是我的生成器产生的数据中的一个优势。 1 条记录的长度为 43 而不是 46，这会影响整个训练。我仍然对ValueError 消息感到困惑，尽管如此。它读作but got array with shape (1,)，实际上它应该读作but got array with shape (43,)

Answer 2

显然，经过一些迭代后，输入数据的形状错误。我怀疑它发生在这里：

 encoded = self.encode_pair(recipe, document)

encode_pair的代码是什么？是否保证encoded[0] 的大小始终为 46？