使用Python对文本文件进行排序

Question

我有一个包含超过1000万行的文本文件.这样的行:

37024469;196672001;255.0000000000
37024469;196665001;396.0000000000
37024469;196664001;396.0000000000
37024469;196399002;85.0000000000
37024469;160507001;264.0000000000
37024469;160506001;264.0000000000

如你所见,分隔符是";".我想根据第二个元素使用python对这个文本文件进行排序.我不能使用拆分功能.因为它会导致MemoryError.我该怎么办呢？

Answer 1

不要在内存中排序1000万行.将其拆分为:

• 运行100个100k行排序(使用文件作为迭代器,结合islice()或类似选择批处理).写出其他地方的文件.

• 合并已排序的文件.这是一个合并生成器,您可以传递100个打开的文件,它将按排序顺序生成行.逐行写入新文件:

  import operator
  
  def mergeiter(*iterables, **kwargs):
      """Given a set of sorted iterables, yield the next value in merged order
  
      Takes an optional `key` callable to compare values by.
      """
      iterables = [iter(it) for it in iterables]
      iterables = {i: [next(it), i, it] for i, it in enumerate(iterables)}
      if 'key' not in kwargs:
          key = operator.itemgetter(0)
      else:
          key = lambda item, key=kwargs['key']: key(item[0])
  
      while True:
          value, i, it = min(iterables.values(), key=key)
          yield value
          try:
              iterables[i][0] = next(it)
          except StopIteration:
              del iterables[i]
              if not iterables:
                  raise
  

Answer 2

基于使用 Python 在 2MB RAM 中对 100 万个 32 位整数进行排序：

import sys
from functools import partial
from heapq import merge
from tempfile import TemporaryFile

# define sorting criteria
def second_column(line, default=float("inf")):
    try:
        return int(line.split(";", 2)[1]) # use int() for numeric sort
    except (IndexError, ValueError):
        return default # a key for non-integer or non-existent 2nd column

# sort lines in small batches, write intermediate results to temporary files
sorted_files = []
nbytes = 1 << 20 # load around nbytes bytes at a time
for lines in iter(partial(sys.stdin.readlines, nbytes), []):
    lines.sort(key=second_column) # sort current batch
    f = TemporaryFile("w+")
    f.writelines(lines)
    f.seek(0) # rewind
    sorted_files.append(f)

# merge & write the result
sys.stdout.writelines(merge(*sorted_files, key=second_column))

# clean up
for f in sorted_files:
    f.close() # temporary file is deleted when it closes

heapq.merge()key从 Python 3.5 开始就有参数。您可以尝试mergeiter()使用 Martijn Pieters 的答案，或者在较旧的 Python 版本上进行Schwartzian 变换：

iters = [((second_column(line), line) for line in file)
         for file in sorted_files] # note: this makes the sort unstable
sorted_lines = (line for _, line in merge(*iters))
sys.stdout.writelines(sorted_lines)

用法：

$ python sort-k2-n.py < input.txt > output.txt