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Questo tutorial di classificazione di testi allena una rete neurale ricorrente sul IMDB filmato di grandi dimensioni commento set di dati per l'analisi sentimento.
Impostare
import numpy as np
import tensorflow_datasets as tfds
import tensorflow as tf
tfds.disable_progress_bar()
Importa matplotlib e creare una funzione di supporto per i grafici trama:
import matplotlib.pyplot as plt
def plot_graphs(history, metric):
plt.plot(history.history[metric])
plt.plot(history.history['val_'+metric], '')
plt.xlabel("Epochs")
plt.ylabel(metric)
plt.legend([metric, 'val_'+metric])
Configurazione della pipeline di input
L'IMDB grande rassegna di film DataSet è un binario di classificazione del set di dati-tutte le recensioni hanno o un sentimento positivo o negativo.
Scarica il set di dati utilizzando TFDS . Vedere l'un'esercitazione di carico per i dettagli su come caricare questo tipo di dati manualmente.
dataset, info = tfds.load('imdb_reviews', with_info=True,
as_supervised=True)
train_dataset, test_dataset = dataset['train'], dataset['test']
train_dataset.element_spec
(TensorSpec(shape=(), dtype=tf.string, name=None), TensorSpec(shape=(), dtype=tf.int64, name=None))
Inizialmente restituisce un set di dati di (testo, coppie di etichette):
for example, label in train_dataset.take(1):
print('text: ', example.numpy())
print('label: ', label.numpy())
text: b"This was an absolutely terrible movie. Don't be lured in by Christopher Walken or Michael Ironside. Both are great actors, but this must simply be their worst role in history. Even their great acting could not redeem this movie's ridiculous storyline. This movie is an early nineties US propaganda piece. The most pathetic scenes were those when the Columbian rebels were making their cases for revolutions. Maria Conchita Alonso appeared phony, and her pseudo-love affair with Walken was nothing but a pathetic emotional plug in a movie that was devoid of any real meaning. I am disappointed that there are movies like this, ruining actor's like Christopher Walken's good name. I could barely sit through it." label: 0
Successivo mischiare i dati per la formazione e creare lotti di queste (text, label) coppie:
BUFFER_SIZE = 10000
BATCH_SIZE = 64
train_dataset = train_dataset.shuffle(BUFFER_SIZE).batch(BATCH_SIZE).prefetch(tf.data.AUTOTUNE)
test_dataset = test_dataset.batch(BATCH_SIZE).prefetch(tf.data.AUTOTUNE)
for example, label in train_dataset.take(1):
print('texts: ', example.numpy()[:3])
print()
print('labels: ', label.numpy()[:3])
texts: [b'This is arguably the worst film I have ever seen, and I have quite an appetite for awful (and good) movies. It could (just) have managed a kind of adolescent humour if it had been consistently tongue-in-cheek --\xc3\xa0 la ROCKY HORROR PICTURE SHOW, which was really very funny. Other movies, like PLAN NINE FROM OUTER SPACE, manage to be funny while (apparently) trying to be serious. As to the acting, it looks like they rounded up brain-dead teenagers and asked them to ad-lib the whole production. Compared to them, Tom Cruise looks like Alec Guinness. There was one decent interpretation -- that of the older ghoul-busting broad on the motorcycle.' b"I saw this film in the worst possible circumstance. I'd already missed 15 minutes when I woke up to it on an international flight between Sydney and Seoul. I didn't know what I was watching, I thought maybe it was a movie of the week, but quickly became riveted by the performance of the lead actress playing a young woman who's child had been kidnapped. The premise started taking twist and turns I didn't see coming and by the end credits I was scrambling through the the in-flight guide to figure out what I had just watched. Turns out I was belatedly discovering Do-yeon Jeon who'd won Best Actress at Cannes for the role. I don't know if Secret Sunshine is typical of Korean cinema but I'm off to the DVD store to discover more." b"Hello. I am Paul Raddick, a.k.a. Panic Attack of WTAF, Channel 29 in Philadelphia. Let me tell you about this god awful movie that powered on Adam Sandler's film career but was digitized after a short time.<br /><br />Going Overboard is about an aspiring comedian played by Sandler who gets a job on a cruise ship and fails...or so I thought. Sandler encounters babes that like History of the World Part 1 and Rebound. The babes were supposed to be engaged, but, actually, they get executed by Sawtooth, the meanest cannibal the world has ever known. Adam Sandler fared bad in Going Overboard, but fared better in Big Daddy, Billy Madison, and Jen Leone's favorite, 50 First Dates. Man, Drew Barrymore was one hot chick. Spanglish is red hot, Going Overboard ain't Dooley squat! End of file."] labels: [0 1 0]
Crea il codificatore di testo
Il testo grezzo caricato da tfds deve essere elaborato prima di poter essere utilizzato in un modello. Il modo più semplice per elaborare testi per la formazione sta usando il TextVectorization layer. Questo livello ha molte funzionalità, ma questo tutorial si attiene al comportamento predefinito.
Creare il livello e passare il testo del set di dati al livello del .adapt metodo:
VOCAB_SIZE = 1000
encoder = tf.keras.layers.TextVectorization(
max_tokens=VOCAB_SIZE)
encoder.adapt(train_dataset.map(lambda text, label: text))
Il .adapt metodo imposta vocabolario del livello. Ecco i primi 20 gettoni. Dopo il padding e i token sconosciuti vengono ordinati per frequenza:
vocab = np.array(encoder.get_vocabulary())
vocab[:20]
array(['', '[UNK]', 'the', 'and', 'a', 'of', 'to', 'is', 'in', 'it', 'i',
'this', 'that', 'br', 'was', 'as', 'for', 'with', 'movie', 'but'],
dtype='<U14')
Una volta impostato il vocabolario, il livello può codificare il testo in indici. I tensori di indici sono 0 imbottito per la sequenza più lunga nel batch (a meno che non si imposta un fisso output_sequence_length ):
encoded_example = encoder(example)[:3].numpy()
encoded_example
array([[ 11, 7, 1, ..., 0, 0, 0],
[ 10, 208, 11, ..., 0, 0, 0],
[ 1, 10, 237, ..., 0, 0, 0]])
Con le impostazioni predefinite, il processo non è completamente reversibile. Ci sono tre ragioni principali per questo:
- Il valore predefinito per
preprocessing.TextVectorizations'standardizeargomento è"lower_and_strip_punctuation". - La dimensione limitata del vocabolario e la mancanza di fallback basati sui caratteri si traducono in alcuni token sconosciuti.
for n in range(3):
print("Original: ", example[n].numpy())
print("Round-trip: ", " ".join(vocab[encoded_example[n]]))
print()
Original: b'This is arguably the worst film I have ever seen, and I have quite an appetite for awful (and good) movies. It could (just) have managed a kind of adolescent humour if it had been consistently tongue-in-cheek --\xc3\xa0 la ROCKY HORROR PICTURE SHOW, which was really very funny. Other movies, like PLAN NINE FROM OUTER SPACE, manage to be funny while (apparently) trying to be serious. As to the acting, it looks like they rounded up brain-dead teenagers and asked them to ad-lib the whole production. Compared to them, Tom Cruise looks like Alec Guinness. There was one decent interpretation -- that of the older ghoul-busting broad on the motorcycle.' Round-trip: this is [UNK] the worst film i have ever seen and i have quite an [UNK] for awful and good movies it could just have [UNK] a kind of [UNK] [UNK] if it had been [UNK] [UNK] [UNK] la [UNK] horror picture show which was really very funny other movies like [UNK] [UNK] from [UNK] space [UNK] to be funny while apparently trying to be serious as to the acting it looks like they [UNK] up [UNK] [UNK] and [UNK] them to [UNK] the whole production [UNK] to them tom [UNK] looks like [UNK] [UNK] there was one decent [UNK] that of the older [UNK] [UNK] on the [UNK] Original: b"I saw this film in the worst possible circumstance. I'd already missed 15 minutes when I woke up to it on an international flight between Sydney and Seoul. I didn't know what I was watching, I thought maybe it was a movie of the week, but quickly became riveted by the performance of the lead actress playing a young woman who's child had been kidnapped. The premise started taking twist and turns I didn't see coming and by the end credits I was scrambling through the the in-flight guide to figure out what I had just watched. Turns out I was belatedly discovering Do-yeon Jeon who'd won Best Actress at Cannes for the role. I don't know if Secret Sunshine is typical of Korean cinema but I'm off to the DVD store to discover more." Round-trip: i saw this film in the worst possible [UNK] id already [UNK] [UNK] minutes when i [UNK] up to it on an [UNK] [UNK] between [UNK] and [UNK] i didnt know what i was watching i thought maybe it was a movie of the [UNK] but quickly became [UNK] by the performance of the lead actress playing a young woman whos child had been [UNK] the premise started taking twist and turns i didnt see coming and by the end credits i was [UNK] through the the [UNK] [UNK] to figure out what i had just watched turns out i was [UNK] [UNK] [UNK] [UNK] [UNK] [UNK] best actress at [UNK] for the role i dont know if secret [UNK] is typical of [UNK] cinema but im off to the dvd [UNK] to [UNK] more Original: b"Hello. I am Paul Raddick, a.k.a. Panic Attack of WTAF, Channel 29 in Philadelphia. Let me tell you about this god awful movie that powered on Adam Sandler's film career but was digitized after a short time.<br /><br />Going Overboard is about an aspiring comedian played by Sandler who gets a job on a cruise ship and fails...or so I thought. Sandler encounters babes that like History of the World Part 1 and Rebound. The babes were supposed to be engaged, but, actually, they get executed by Sawtooth, the meanest cannibal the world has ever known. Adam Sandler fared bad in Going Overboard, but fared better in Big Daddy, Billy Madison, and Jen Leone's favorite, 50 First Dates. Man, Drew Barrymore was one hot chick. Spanglish is red hot, Going Overboard ain't Dooley squat! End of file." Round-trip: [UNK] i am paul [UNK] [UNK] [UNK] [UNK] of [UNK] [UNK] [UNK] in [UNK] let me tell you about this god awful movie that [UNK] on [UNK] [UNK] film career but was [UNK] after a short [UNK] br going [UNK] is about an [UNK] [UNK] played by [UNK] who gets a job on a [UNK] [UNK] and [UNK] so i thought [UNK] [UNK] [UNK] that like history of the world part 1 and [UNK] the [UNK] were supposed to be [UNK] but actually they get [UNK] by [UNK] the [UNK] [UNK] the world has ever known [UNK] [UNK] [UNK] bad in going [UNK] but [UNK] better in big [UNK] [UNK] [UNK] and [UNK] [UNK] favorite [UNK] first [UNK] man [UNK] [UNK] was one hot [UNK] [UNK] is red hot going [UNK] [UNK] [UNK] [UNK] end of [UNK]
Crea il modello
Sopra c'è uno schema del modello.
Questo modello può essere accumulo come
tf.keras.Sequential.Il primo strato è l'
encoder, che converte il testo in una sequenza di indici di token.Dopo l'encoder c'è un livello di incorporamento. Un livello di incorporamento memorizza un vettore per parola. Quando viene chiamato, converte le sequenze di indici di parole in sequenze di vettori. Questi vettori sono addestrabili. Dopo l'addestramento (su dati sufficienti), le parole con significati simili hanno spesso vettori simili.
Questo indice-ricerca è molto più efficiente rispetto al funzionamento equivalente di passare un vettore codificato un caldo attraverso un
tf.keras.layers.Densestrato.Una rete neurale ricorrente (RNN) elabora l'input di sequenza iterando attraverso gli elementi. Gli RNN passano gli output da un timestep al loro input nel timestep successivo.
Il
tf.keras.layers.Bidirectionalavvolgitore può essere utilizzato anche con uno strato RNN. Questo propaga l'input avanti e indietro attraverso il livello RNN e quindi concatena l'output finale.Il vantaggio principale di un RNN bidirezionale è che il segnale dall'inizio dell'input non ha bisogno di essere elaborato fino in fondo ad ogni timestep per influenzare l'output.
Il principale svantaggio di un RNN bidirezionale è che non è possibile trasmettere in modo efficiente le previsioni mentre le parole vengono aggiunte alla fine.
Dopo la RNN ha convertito la sequenza di un singolo vettore due
layers.Densefare qualche lavorazione finale, e convertito da questa rappresentazione vettoriale per un singolo logit come l'uscita classificazione.
Il codice per implementarlo è il seguente:
model = tf.keras.Sequential([
encoder,
tf.keras.layers.Embedding(
input_dim=len(encoder.get_vocabulary()),
output_dim=64,
# Use masking to handle the variable sequence lengths
mask_zero=True),
tf.keras.layers.Bidirectional(tf.keras.layers.LSTM(64)),
tf.keras.layers.Dense(64, activation='relu'),
tf.keras.layers.Dense(1)
])
Si prega di notare che qui viene utilizzato il modello sequenziale Keras poiché tutti i livelli nel modello hanno solo un singolo input e producono un singolo output. Nel caso in cui desideri utilizzare il livello RNN con stato, potresti voler creare il tuo modello con l'API funzionale Keras o la sottoclasse del modello in modo da poter recuperare e riutilizzare gli stati del livello RNN. Si prega di verificare guida Keras RNN per maggiori dettagli.
Lo strato embedding usi mascheramento per gestire le diverse lunghezze di sequenza. Tutti gli strati dopo l' Embedding supporto di mascheramento:
print([layer.supports_masking for layer in model.layers])
[False, True, True, True, True]
Per confermare che funziona come previsto, valuta una frase due volte. Innanzitutto, da solo, quindi non ci sono imbottiture da mascherare:
# predict on a sample text without padding.
sample_text = ('The movie was cool. The animation and the graphics '
'were out of this world. I would recommend this movie.')
predictions = model.predict(np.array([sample_text]))
print(predictions[0])
[-0.00012211]
Ora, valutalo di nuovo in un batch con una frase più lunga. Il risultato dovrebbe essere identico:
# predict on a sample text with padding
padding = "the " * 2000
predictions = model.predict(np.array([sample_text, padding]))
print(predictions[0])
[-0.00012211]
Compila il modello Keras per configurare il processo di formazione:
model.compile(loss=tf.keras.losses.BinaryCrossentropy(from_logits=True),
optimizer=tf.keras.optimizers.Adam(1e-4),
metrics=['accuracy'])
Allena il modello
history = model.fit(train_dataset, epochs=10,
validation_data=test_dataset,
validation_steps=30)
Epoch 1/10 391/391 [==============================] - 39s 84ms/step - loss: 0.6454 - accuracy: 0.5630 - val_loss: 0.4888 - val_accuracy: 0.7568 Epoch 2/10 391/391 [==============================] - 30s 75ms/step - loss: 0.3925 - accuracy: 0.8200 - val_loss: 0.3663 - val_accuracy: 0.8464 Epoch 3/10 391/391 [==============================] - 30s 75ms/step - loss: 0.3319 - accuracy: 0.8525 - val_loss: 0.3402 - val_accuracy: 0.8385 Epoch 4/10 391/391 [==============================] - 30s 75ms/step - loss: 0.3183 - accuracy: 0.8616 - val_loss: 0.3289 - val_accuracy: 0.8438 Epoch 5/10 391/391 [==============================] - 30s 75ms/step - loss: 0.3088 - accuracy: 0.8656 - val_loss: 0.3254 - val_accuracy: 0.8646 Epoch 6/10 391/391 [==============================] - 32s 81ms/step - loss: 0.3043 - accuracy: 0.8686 - val_loss: 0.3242 - val_accuracy: 0.8521 Epoch 7/10 391/391 [==============================] - 30s 76ms/step - loss: 0.3019 - accuracy: 0.8696 - val_loss: 0.3315 - val_accuracy: 0.8609 Epoch 8/10 391/391 [==============================] - 32s 76ms/step - loss: 0.3007 - accuracy: 0.8688 - val_loss: 0.3245 - val_accuracy: 0.8609 Epoch 9/10 391/391 [==============================] - 31s 77ms/step - loss: 0.2981 - accuracy: 0.8707 - val_loss: 0.3294 - val_accuracy: 0.8599 Epoch 10/10 391/391 [==============================] - 31s 78ms/step - loss: 0.2969 - accuracy: 0.8742 - val_loss: 0.3218 - val_accuracy: 0.8547
test_loss, test_acc = model.evaluate(test_dataset)
print('Test Loss:', test_loss)
print('Test Accuracy:', test_acc)
391/391 [==============================] - 15s 38ms/step - loss: 0.3185 - accuracy: 0.8582 Test Loss: 0.3184521794319153 Test Accuracy: 0.8581600189208984
plt.figure(figsize=(16, 8))
plt.subplot(1, 2, 1)
plot_graphs(history, 'accuracy')
plt.ylim(None, 1)
plt.subplot(1, 2, 2)
plot_graphs(history, 'loss')
plt.ylim(0, None)
(0.0, 0.6627909764647484)
Esegui una previsione su una nuova frase:
Se la previsione è >= 0,0, è positiva altrimenti è negativa.
sample_text = ('The movie was cool. The animation and the graphics '
'were out of this world. I would recommend this movie.')
predictions = model.predict(np.array([sample_text]))
Impila due o più livelli LSTM
KERAS strati ricorrenti hanno due modalità disponibili che sono controllati dal return_sequences argomento del costruttore:
Se
Falserestituisce solo l'ultima uscita per ogni sequenza di ingresso (un tensore 2D di forma (batch_size, output_features)). Questa è l'impostazione predefinita, utilizzata nel modello precedente.Se
Truele sequenze complete di uscite consecutive per ogni passo temporale viene restituito (un tensore 3D di forma(batch_size, timesteps, output_features)).
Ecco ciò che il flusso di sguardi di informazione come con return_sequences=True :
La cosa interessante sull'utilizzo di un RNN con return_sequences=True è che l'uscita ha ancora 3 assi, come l'ingresso, in modo che possa essere trasmesso ad un altro strato RNN, in questo modo:
model = tf.keras.Sequential([
encoder,
tf.keras.layers.Embedding(len(encoder.get_vocabulary()), 64, mask_zero=True),
tf.keras.layers.Bidirectional(tf.keras.layers.LSTM(64, return_sequences=True)),
tf.keras.layers.Bidirectional(tf.keras.layers.LSTM(32)),
tf.keras.layers.Dense(64, activation='relu'),
tf.keras.layers.Dropout(0.5),
tf.keras.layers.Dense(1)
])
model.compile(loss=tf.keras.losses.BinaryCrossentropy(from_logits=True),
optimizer=tf.keras.optimizers.Adam(1e-4),
metrics=['accuracy'])
history = model.fit(train_dataset, epochs=10,
validation_data=test_dataset,
validation_steps=30)
Epoch 1/10 391/391 [==============================] - 71s 149ms/step - loss: 0.6502 - accuracy: 0.5625 - val_loss: 0.4923 - val_accuracy: 0.7573 Epoch 2/10 391/391 [==============================] - 55s 138ms/step - loss: 0.4067 - accuracy: 0.8198 - val_loss: 0.3727 - val_accuracy: 0.8271 Epoch 3/10 391/391 [==============================] - 54s 136ms/step - loss: 0.3417 - accuracy: 0.8543 - val_loss: 0.3343 - val_accuracy: 0.8510 Epoch 4/10 391/391 [==============================] - 53s 134ms/step - loss: 0.3242 - accuracy: 0.8607 - val_loss: 0.3268 - val_accuracy: 0.8568 Epoch 5/10 391/391 [==============================] - 53s 135ms/step - loss: 0.3174 - accuracy: 0.8652 - val_loss: 0.3213 - val_accuracy: 0.8516 Epoch 6/10 391/391 [==============================] - 52s 132ms/step - loss: 0.3098 - accuracy: 0.8671 - val_loss: 0.3294 - val_accuracy: 0.8547 Epoch 7/10 391/391 [==============================] - 53s 134ms/step - loss: 0.3063 - accuracy: 0.8697 - val_loss: 0.3158 - val_accuracy: 0.8594 Epoch 8/10 391/391 [==============================] - 52s 132ms/step - loss: 0.3043 - accuracy: 0.8692 - val_loss: 0.3184 - val_accuracy: 0.8521 Epoch 9/10 391/391 [==============================] - 53s 133ms/step - loss: 0.3016 - accuracy: 0.8704 - val_loss: 0.3208 - val_accuracy: 0.8609 Epoch 10/10 391/391 [==============================] - 54s 136ms/step - loss: 0.2975 - accuracy: 0.8740 - val_loss: 0.3301 - val_accuracy: 0.8651
test_loss, test_acc = model.evaluate(test_dataset)
print('Test Loss:', test_loss)
print('Test Accuracy:', test_acc)
391/391 [==============================] - 26s 65ms/step - loss: 0.3293 - accuracy: 0.8646 Test Loss: 0.329334557056427 Test Accuracy: 0.8646399974822998
# predict on a sample text without padding.
sample_text = ('The movie was not good. The animation and the graphics '
'were terrible. I would not recommend this movie.')
predictions = model.predict(np.array([sample_text]))
print(predictions)
[[-1.6796288]]
plt.figure(figsize=(16, 6))
plt.subplot(1, 2, 1)
plot_graphs(history, 'accuracy')
plt.subplot(1, 2, 2)
plot_graphs(history, 'loss')
Scopri altri strati ricorrenti esistenti, come strati GRU .
Se stai interestied nella costruzione di RNR personalizzati, consultare la Guida Keras RNN .