ptb_reader源码解析

# Copyright 2015 The TensorFlow Authors. All Rights Reserved.
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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#     http://www.apache.org/licenses/LICENSE-2.0
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"""Utilities for parsing PTB text files."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import collections
import os

import numpy as np
import tensorflow as tf


def _read_words(filename):
  with tf.gfile.GFile(filename, "r") as f:
    return f.read().replace("\n", "<eos>").split() #读取文件， 将换行符替换为 <eos>， 然后将文件按空格分割。 返回一个 1-D list


def _build_vocab(filename):  #用于建立字典
  data = _read_words(filename)
  counter = collections.Counter(data) #输出一个字典： key是word， value是这个word出现的次数
  count_pairs = sorted(counter.items(), key=lambda x: (-x[1], x[0]))
#counter.items() 会返回一个tuple列表， tuple是(key, value), 按 value的降序，key的升序排列
  words, _ = list(zip(*count_pairs)) #感觉这个像unzip 就是把key放在一个tuple里，value放在一个tuple里
  word_to_id = dict(zip(words, range(len(words))))#对每个word进行编号， 按照之前words输出的顺序（value降序，key升序）
  return word_to_id  #返回dict， key：word， value：id


def _file_to_word_ids(filename, word_to_id): #将file表示为word_id的形式
  data = _read_words(filename)
  return [word_to_id[word] for word in data]

def ptb_raw_data(data_path=None):
  """Load PTB raw data from data directory "data_path".
  Reads PTB text files, converts strings to integer ids,
  and performs mini-batching of the inputs.
  The PTB dataset comes from Tomas Mikolov's webpage:
  http://www.fit.vutbr.cz/~imikolov/rnnlm/simple-examples.tgz
  Args:
    data_path: string path to the directory where simple-examples.tgz has
      been extracted.
  Returns:
    tuple (train_data, valid_data, test_data, vocabulary)
    where each of the data objects can be passed to PTBIterator.
  """

  train_path = os.path.join(data_path, "ptb.train.txt")
  valid_path = os.path.join(data_path, "ptb.valid.txt")
  test_path = os.path.join(data_path, "ptb.test.txt")

  word_to_id = _build_vocab(train_path) #使用训练集确定word id
  train_data = _file_to_word_ids(train_path, word_to_id)
  valid_data = _file_to_word_ids(valid_path, word_to_id)
  test_data = _file_to_word_ids(test_path, word_to_id)
  vocabulary = len(word_to_id)#字典的大小
  return train_data, valid_data, test_data, vocabulary


def ptb_iterator(raw_data, batch_size, num_steps):
  """Iterate on the raw PTB data.
  This generates batch_size pointers into the raw PTB data, and allows
  minibatch iteration along these pointers.
  Args:
    raw_data: one of the raw data outputs from ptb_raw_data.
    batch_size: int, the batch size.
    num_steps: int, the number of unrolls.
  Yields:
    Pairs of the batched data, each a matrix of shape [batch_size, num_steps].
    The second element of the tuple is the same data time-shifted to the
    right by one.
  Raises:
    ValueError: if batch_size or num_steps are too high.
  """
  raw_data = np.array(raw_data, dtype=np.int32)#raw data : train_data | vali_data | test data

  data_len = len(raw_data) #how many words in the data_set
  batch_len = data_len // batch_size
  data = np.zeros([batch_size, batch_len], dtype=np.int32)#batch_len 就是几个word的意思
  for i in range(batch_size):
    data[i] = raw_data[batch_len * i:batch_len * (i + 1)]

  epoch_size = (batch_len - 1) // num_steps

  if epoch_size == 0:
    raise ValueError("epoch_size == 0, decrease batch_size or num_steps")

  for i in range(epoch_size):
    x = data[:, i*num_steps:(i+1)*num_steps]
    y = data[:, i*num_steps+1:(i+1)*num_steps+1]
  yield (x, y)