tensorflow2系類知識-4 ：RNN

循環神經網絡（RNN）

• 循環神經網絡（Recurrent Neural Network, RNN）是一種適宜於處理序列數據的神經網絡，被廣泛用於語言模型、文本生成、機器翻譯等。

示例代碼

# -*- coding:utf-8 -*-
# /usr/bin/python
'''
-------------------------------------------------
   File Name   :  RNN
   Description :  AIM: 
                  Functions: 1. 基本原理
                             2. 概念
                             3. 示例代碼
   Envs        :  python == 3.7
                  pip install tensorflow==2.1.0 -i https://pypi.douban.com/simple
   Author      :  errol
   Date        :  2020/5/2  15:20
   CodeStyle   :  規範,簡潔,易懂,可閱讀,可維護,可移植!
-------------------------------------------------
   Change Activity:
          2020/5/2 : text
-------------------------------------------------
'''

import numpy as np
import tensorflow as tf

class DataLoader(object):

    def __init__(self,):
        path = tf.keras.utils.get_file('nietzsche.txt',
            origin='https://s3.amazonaws.com/text-datasets/nietzsche.txt')

        with open(path, encoding='utf-8') as file:
            self.raw_text = file.read().lower()
        self.chars = sorted(list(set(self.raw_text)))
        self.char_indices = dic((c,i) for i,c in enumerate(self.chars))
        self.indices_char = dict((i, c) for i, c in enumerate(self.chars))
        self.text = [self.char_indices[c] for c in self.raw_text]

    def get_batch(self, seq_length, batch_size):
        seq = []
        next_char = []
        for i in range(batch_size):
            index = np.random.randint(0, len(self.text) - seq_length)
            seq.append(self.text[index:index + seq_length])
            next_char.append(self.text[index + seq_length])
        return np.array(seq), np.array(next_char)  # [batch_size, seq_length], [num_batch]

class RNN(tf.keras.Model):

    def __init__(self,num_chars,batch_size,seq_length):
        super().__init__()
        self.num_chars = num_chars
        self.seq_length = seq_length
        self.batch_size = batch_size
        self.cell = tf.keras.layers.LSTMCell(units=256)
        self.dense = tf.keras.layers.Dense(units=self.num_chars)

    def call(self,inputs,from_logits=False):
        inputs = tf.one_hot(inputs,depth=self.num_chars)
        state = self.cell.get_initial_state(batch_size=self.batch_size,dtype=tf.float32)
        for i in range(self.seq_length):
            output,stat = self.cell(inputs[:,t,:],state)
        logits =self.dense(output)
        if from_logits:
            return logits
        else:
            return tf.nn.softmax(logits)


num_batches = 1000
seq_length = 40
batch_size = 50
learning_rate = 1e-3
'''
從 DataLoader 中隨機取一批訓練數據；
將這批數據送入模型，計算出模型的預測值；
將模型預測值與真實值進行比較，計算損失函數（loss）；
計算損失函數關於模型變量的導數；
使用優化器更新模型參數以最小化損失函數。
'''
data_loader = DataLoader()
model = RNN(num_chars=len(data_loader.chars), batch_size=batch_size, seq_length=seq_length)
optimizer = tf.keras.optimizers.Adam(learning_rate=learning_rate)
for batch_index in range(num_batches):
    X, y = data_loader.get_batch(seq_length, batch_size)
    with tf.GradientTape() as tape:
        y_pred = model(X)
        loss = tf.keras.losses.sparse_categorical_crossentropy(y_true=y, y_pred=y_pred)
        loss = tf.reduce_mean(loss)
        print("batch %d: loss %f" % (batch_index, loss.numpy()))
    grads = tape.gradient(loss, model.variables)
    optimizer.apply_gradients(grads_and_vars=zip(grads, model.variables))


def predict(self, inputs, temperature=1.):
    batch_size, _ = tf.shape(inputs)
    logits = self(inputs, from_logits=True)
    prob = tf.nn.softmax(logits / temperature).numpy()
    return np.array([np.random.choice(self.num_chars, p=prob[i, :])
                     for i in range(batch_size.numpy())])

X_, _ = data_loader.get_batch(seq_length, 1)
for diversity in [0.2, 0.5, 1.0, 1.2]:
    X = X_
    print("diversity %f:" % diversity)
    for t in range(400):
        y_pred = model.predict(X, diversity)
        print(data_loader.indices_char[y_pred[0]], end='', flush=True)
        X = np.concatenate([X[:, 1:], np.expand_dims(y_pred, axis=1)], axis=-1)
    print("\n")

瞭解本專欄 訂閱專欄 解鎖全文