batch很好理解,就是batch size。注意在一个epoch中最后一个batch大小可能小于等于batch size
dataset.repeat就是俗称epoch,但在tf中与dataset.shuffle的使用顺序可能会导致个epoch的混合
dataset.shuffle就是说维持一个buffer size 大小的 shuffle buffer,图中所需的每个样本从shuffle buffer中获取,取得一个样本后,就从源数据集中加入一个样本到shuffle buffer中。
import os
os.environ['CUDA_VISIBLE_DEVICES'] = ""
import numpy as np
import tensorflow as tf
np.random.seed(0)
x = np.random.sample((11,2))
# make a dataset from a numpy array
print(x)
print()
dataset = tf.data.Dataset.from_tensor_slices(x)
dataset = dataset.shuffle(3)
dataset = dataset.batch(4)
dataset = dataset.repeat(2)
# create the iterator
iter = dataset.make_one_shot_iterator()
el = iter.get_next()
with tf.Session() as sess:
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
#源数据集
[[ 0.5488135 0.71518937]
[ 0.60276338 0.54488318]
[ 0.4236548 0.64589411]
[ 0.43758721 0.891773 ]
[ 0.96366276 0.38344152]
[ 0.79172504 0.52889492]
[ 0.56804456 0.92559664]
[ 0.07103606 0.0871293 ]
[ 0.0202184 0.83261985]
[ 0.77815675 0.87001215]
[ 0.97861834 0.79915856]]
# 通过shuffle batch后取得的样本
[[ 0.4236548 0.64589411]
[ 0.60276338 0.54488318]
[ 0.43758721 0.891773 ]
[ 0.5488135 0.71518937]]
[[ 0.96366276 0.38344152]
[ 0.56804456 0.92559664]
[ 0.0202184 0.83261985]
[ 0.79172504 0.52889492]]
[[ 0.07103606 0.0871293 ]
[ 0.97861834 0.79915856]
[ 0.77815675 0.87001215]] #最后一个batch样本个数为3
[[ 0.60276338 0.54488318]
[ 0.5488135 0.71518937]
[ 0.43758721 0.891773 ]
[ 0.79172504 0.52889492]]
[[ 0.4236548 0.64589411]
[ 0.56804456 0.92559664]
[ 0.0202184 0.83261985]
[ 0.07103606 0.0871293 ]]
[[ 0.77815675 0.87001215]
[ 0.96366276 0.38344152]
[ 0.97861834 0.79915856]] #最后一个batch样本个数为3
1、按照shuffle中设置的buffer size,首先从源数据集取得三个样本: shuffle buffer: [ 0.5488135 0.71518937] [ 0.60276338 0.54488318] [ 0.4236548 0.64589411] 2、从buffer中取一个样本到batch中得: shuffle buffer: [ 0.5488135 0.71518937] [ 0.60276338 0.54488318] batch: [ 0.4236548 0.64589411] 3、shuffle buffer不足三个样本,从源数据集提取一个样本: shuffle buffer: [ 0.5488135 0.71518937] [ 0.60276338 0.54488318] [ 0.43758721 0.891773 ] 4、从buffer中取一个样本到batch中得: shuffle buffer: [ 0.5488135 0.71518937] [ 0.43758721 0.891773 ] batch: [ 0.4236548 0.64589411] [ 0.60276338 0.54488318] 5、如此反复。这就意味中如果shuffle 的buffer size=1,数据集不打乱。如果shuffle 的buffer size=数据集样本数量,随机打乱整个数据集
import os
os.environ['CUDA_VISIBLE_DEVICES'] = ""
import numpy as np
import tensorflow as tf
np.random.seed(0)
x = np.random.sample((11,2))
# make a dataset from a numpy array
print(x)
print()
dataset = tf.data.Dataset.from_tensor_slices(x)
dataset = dataset.shuffle(1)
dataset = dataset.batch(4)
dataset = dataset.repeat(2)
# create the iterator
iter = dataset.make_one_shot_iterator()
el = iter.get_next()
with tf.Session() as sess:
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
[[ 0.5488135 0.71518937]
[ 0.60276338 0.54488318]
[ 0.4236548 0.64589411]
[ 0.43758721 0.891773 ]
[ 0.96366276 0.38344152]
[ 0.79172504 0.52889492]
[ 0.56804456 0.92559664]
[ 0.07103606 0.0871293 ]
[ 0.0202184 0.83261985]
[ 0.77815675 0.87001215]
[ 0.97861834 0.79915856]]
[[ 0.5488135 0.71518937]
[ 0.60276338 0.54488318]
[ 0.4236548 0.64589411]
[ 0.43758721 0.891773 ]]
[[ 0.96366276 0.38344152]
[ 0.79172504 0.52889492]
[ 0.56804456 0.92559664]
[ 0.07103606 0.0871293 ]]
[[ 0.0202184 0.83261985]
[ 0.77815675 0.87001215]
[ 0.97861834 0.79915856]]
[[ 0.5488135 0.71518937]
[ 0.60276338 0.54488318]
[ 0.4236548 0.64589411]
[ 0.43758721 0.891773 ]]
[[ 0.96366276 0.38344152]
[ 0.79172504 0.52889492]
[ 0.56804456 0.92559664]
[ 0.07103606 0.0871293 ]]
[[ 0.0202184 0.83261985]
[ 0.77815675 0.87001215]
[ 0.97861834 0.79915856]]
注意如果repeat在shuffle之前使用:
官方说repeat在shuffle之前使用能提高性能,但模糊了数据样本的epoch关系
import os
os.environ['CUDA_VISIBLE_DEVICES'] = ""
import numpy as np
import tensorflow as tf
np.random.seed(0)
x = np.random.sample((11,2))
# make a dataset from a numpy array
print(x)
print()
dataset = tf.data.Dataset.from_tensor_slices(x)
dataset = dataset.repeat(2)
dataset = dataset.shuffle(11)
dataset = dataset.batch(4)
# create the iterator
iter = dataset.make_one_shot_iterator()
el = iter.get_next()
with tf.Session() as sess:
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
print(sess.run(el))
[[ 0.5488135 0.71518937]
[ 0.60276338 0.54488318]
[ 0.4236548 0.64589411]
[ 0.43758721 0.891773 ]
[ 0.96366276 0.38344152]
[ 0.79172504 0.52889492]
[ 0.56804456 0.92559664]
[ 0.07103606 0.0871293 ]
[ 0.0202184 0.83261985]
[ 0.77815675 0.87001215]
[ 0.97861834 0.79915856]]
[[ 0.56804456 0.92559664]
[ 0.5488135 0.71518937]
[ 0.60276338 0.54488318]
[ 0.07103606 0.0871293 ]]
[[ 0.96366276 0.38344152]
[ 0.43758721 0.891773 ]
[ 0.43758721 0.891773 ]
[ 0.77815675 0.87001215]]
[[ 0.79172504 0.52889492] #出现相同样本出现在同一个batch中
[ 0.79172504 0.52889492]
[ 0.60276338 0.54488318]
[ 0.4236548 0.64589411]]
[[ 0.07103606 0.0871293 ]
[ 0.4236548 0.64589411]
[ 0.96366276 0.38344152]
[ 0.5488135 0.71518937]]
[[ 0.97861834 0.79915856]
[ 0.0202184 0.83261985]
[ 0.77815675 0.87001215]
[ 0.56804456 0.92559664]]
[[ 0.0202184 0.83261985]
[ 0.97861834 0.79915856]] #可以看到最后个batch为2,而前面都是4
使用案例:
def input_fn(filenames, batch_size=32, num_epochs=1, perform_shuffle=False):
print('Parsing', filenames)
def decode_libsvm(line):
#columns = tf.decode_csv(value, record_defaults=CSV_COLUMN_DEFAULTS)
#features = dict(zip(CSV_COLUMNS, columns))
#labels = features.pop(LABEL_COLUMN)
columns = tf.string_split([line], ' ')
labels = tf.string_to_number(columns.values[0], out_type=tf.float32)
splits = tf.string_split(columns.values[1:], ':')
id_vals = tf.reshape(splits.values,splits.dense_shape)
feat_ids, feat_vals = tf.split(id_vals,num_or_size_splits=2,axis=1)
feat_ids = tf.string_to_number(feat_ids, out_type=tf.int32)
feat_vals = tf.string_to_number(feat_vals, out_type=tf.float32)
#feat_ids = tf.reshape(feat_ids,shape=[-1,FLAGS.field_size])
#for i in range(splits.dense_shape.eval()[0]):
# feat_ids.append(tf.string_to_number(splits.values[2*i], out_type=tf.int32))
# feat_vals.append(tf.string_to_number(splits.values[2*i+1]))
#return tf.reshape(feat_ids,shape=[-1,field_size]), tf.reshape(feat_vals,shape=[-1,field_size]), labels
return {"feat_ids": feat_ids, "feat_vals": feat_vals}, labels
# Extract lines from input files using the Dataset API, can pass one filename or filename list
dataset = tf.data.TextLineDataset(filenames).map(decode_libsvm, num_parallel_calls=10).prefetch(500000) # multi-thread pre-process then prefetch
# Randomizes input using a window of 256 elements (read into memory)
if perform_shuffle:
dataset = dataset.shuffle(buffer_size=256)
# epochs from blending together.
dataset = dataset.repeat(num_epochs)
dataset = dataset.batch(batch_size) # Batch size to use
#return dataset.make_one_shot_iterator()
iterator = dataset.make_one_shot_iterator()
batch_features, batch_labels = iterator.get_next()
#return tf.reshape(batch_ids,shape=[-1,field_size]), tf.reshape(batch_vals,shape=[-1,field_size]), batch_labels
return batch_features, batch_labels
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