只是使用 Google Colab 进行的一个小观察。根据docs https://www.tensorflow.org/api_docs/python/tf/data/Dataset?version=nightly#cache:
注意:为了最终确定缓存,必须完整迭代输入数据集。否则,后续迭代将不会使用缓存数据。
And
注意:缓存每次都会产生完全相同的元素
迭代数据集。如果您希望随机化迭代
order,确保在调用cache之后调用shuffle。
我确实注意到在事先使用缓存和迭代数据集时存在一些差异。这是一个例子。
准备数据:
import random
import struct
import tensorflow as tf
import numpy as np
RAW_N = 2 + 20*20 + 1
bytess = random.sample(range(1, 5000), RAW_N*4)
with open('mydata.bin', 'wb') as f:
f.write(struct.pack('1612i', *bytess))
def decode_and_prepare(register):
register = tf.io.decode_raw(register, out_type=tf.float32)
inputs = register[2:402]
label = tf.random.uniform(()) + register[402:]
return inputs, label
raw_dataset = tf.data.FixedLengthRecordDataset(filenames=['/content/mydata.bin']*7000, record_bytes=RAW_N*4)
raw_dataset = raw_dataset.map(decode_and_prepare)
火车模型without预先缓存和迭代:
total_data_entries = len(list(raw_dataset.map(lambda x, y: (x, y))))
train_ds = raw_dataset.shuffle(buffer_size=total_data_entries).batch(32).prefetch(tf.data.AUTOTUNE)
inputs = tf.keras.layers.Input((400,))
x = tf.keras.layers.Dense(200, activation='relu', kernel_initializer='normal')(inputs)
x = tf.keras.layers.Dense(100, activation='relu', kernel_initializer='normal')(x)
outputs = tf.keras.layers.Dense(1, kernel_initializer='normal')(x)
model = tf.keras.Model(inputs, outputs)
model.compile(optimizer='adam', loss='mse')
model.fit(train_ds, epochs=5)
Epoch 1/5
875/875 [==============================] - 4s 3ms/step - loss: 0.1425
Epoch 2/5
875/875 [==============================] - 4s 3ms/step - loss: 0.0841
Epoch 3/5
875/875 [==============================] - 4s 3ms/step - loss: 0.0840
Epoch 4/5
875/875 [==============================] - 4s 3ms/step - loss: 0.0840
Epoch 5/5
875/875 [==============================] - 4s 3ms/step - loss: 0.0840
<keras.callbacks.History at 0x7fc41be037d0>
训练模型with缓存但是no迭代:
total_data_entries = len(list(raw_dataset.map(lambda x, y: (x, y))))
train_ds = raw_dataset.shuffle(buffer_size=total_data_entries).cache().batch(32).prefetch(tf.data.AUTOTUNE)
inputs = tf.keras.layers.Input((400,))
x = tf.keras.layers.Dense(200, activation='relu', kernel_initializer='normal')(inputs)
x = tf.keras.layers.Dense(100, activation='relu', kernel_initializer='normal')(x)
outputs = tf.keras.layers.Dense(1, kernel_initializer='normal')(x)
model = tf.keras.Model(inputs, outputs)
model.compile(optimizer='adam', loss='mse')
model.fit(train_ds, epochs=5)
Epoch 1/5
875/875 [==============================] - 4s 2ms/step - loss: 0.1428
Epoch 2/5
875/875 [==============================] - 2s 2ms/step - loss: 0.0841
Epoch 3/5
875/875 [==============================] - 2s 2ms/step - loss: 0.0840
Epoch 4/5
875/875 [==============================] - 2s 2ms/step - loss: 0.0840
Epoch 5/5
875/875 [==============================] - 2s 3ms/step - loss: 0.0840
<keras.callbacks.History at 0x7fc41fa87810>
训练模型with缓存和迭代:
total_data_entries = len(list(raw_dataset.map(lambda x, y: (x, y))))
train_ds = raw_dataset.shuffle(buffer_size=total_data_entries).cache().batch(32).prefetch(tf.data.AUTOTUNE)
_ = list(train_ds.as_numpy_iterator()) # iterate dataset beforehand
inputs = tf.keras.layers.Input((400,))
x = tf.keras.layers.Dense(200, activation='relu', kernel_initializer='normal')(inputs)
x = tf.keras.layers.Dense(100, activation='relu', kernel_initializer='normal')(x)
outputs = tf.keras.layers.Dense(1, kernel_initializer='normal')(x)
model = tf.keras.Model(inputs, outputs)
model.compile(optimizer='adam', loss='mse')
model.fit(train_ds, epochs=5)
Epoch 1/5
875/875 [==============================] - 3s 3ms/step - loss: 0.1427
Epoch 2/5
875/875 [==============================] - 2s 2ms/step - loss: 0.0841
Epoch 3/5
875/875 [==============================] - 2s 2ms/step - loss: 0.0840
Epoch 4/5
875/875 [==============================] - 2s 2ms/step - loss: 0.0840
Epoch 5/5
875/875 [==============================] - 2s 2ms/step - loss: 0.0840
<keras.callbacks.History at 0x7fc41ac9c850>
结论:数据集的缓存和先前迭代似乎对训练有影响,但在本例中仅使用了 7000 个文件。