将文本数据库分成 N 个相等的块并保留标题

我有几个大型（30+ 百万行）文本数据库，我正在使用以下代码清理它们，我需要将文件拆分为 100 万行或更少，并保留标题行。我查看了 chunk 和 itertools 但无法得到明确的解决方案。它用于 arcgis 模型。

== 根据 icyrock.com 的响应更新了代码

import arcpy, os
#fc = arcpy.GetParameter(0)
#chunk_size = arcpy.GetParameter(1) # number of records in each dataset

fc='input.txt'
Name = fc[:fc.rfind('.')]
fl = Name+'_db.txt'

with open(fc) as f:
  lines = f.readlines()
lines[:] = lines[3:]
lines[0] = lines[0].replace('Rx(db)', 'Rx_'+Name)
lines[0] = lines[0].replace('Best Unit', 'Best_Unit')
records = len(lines)
with open(fl, 'w') as f: #where N is the chunk number
  f.write('\n'.join(lines))

with open(fl) as file:
  lines = file.readlines()

headers = lines[0:1]
rest = lines[1:]
chunk_size = 1000000

def chunks(lst, chunk_size):
  for i in xrange(0, len(lst), chunk_size):
    yield lst[i:i + chunk_size]

def write_rows(rows, file):
  for row in rows:
    file.write('%s' % row)

part = 1
for chunk in chunks(rest, chunk_size):
  with open(Name+'_%d' % part+'.txt', 'w') as file:
    write_rows(headers, file)
    write_rows(chunk, file)
  part += 1

See 从 python 中的大型文本文件中删除特定行 and 将大型文本 (xyz) 数据库拆分为 x 个相等的部分为背景。我不再需要基于 cygwin 的解决方案，因为它使模型过于复杂。我需要一种Pythonic方式。我们可以使用“记录”来迭代，但不清楚的是如何指定 db #1 中的第 1:999,999 行，db#2 中的第 1,000,0000 到 1,999,999 行等。如果最后一个数据集小于 1m 就可以了记录。

500mb 文件出错（我有 16GB RAM）。

回溯（最近一次调用最后一次）：文件 “P：\ 2012 \ Job_044_DM_Radio_Propogation \工作\测试\ clean_file.py”， 第 10 行，在 行 = f.readlines() MemoryError

记录 2249878

上面的记录量不是总记录数，它只是内存不足的地方（我认为）。

=== 使用 Icyrock 的新代码。

该块似乎工作正常，但在 Arcgis 中使用时出现错误。

开始时间：2012 年 3 月 9 日星期五 17:20:04 警告 000594：输入功能 1945882430：落在输出几何域之外。警告 000595： d:\Temp\cb_vhn007_1.txt_Features1.fid 包含完整列表 无法复制的功能。

我知道这是分块的问题，因为“创建事件层”过程可以很好地处理完整的预分块数据集。

有任何想法吗？

你可以这样做：

with open('file') as file:
  lines = file.readlines()

headers = lines[0:1]
rest = lines[1:]
chunk_size = 4

def chunks(lst, chunk_size):
  for i in xrange(0, len(lst), chunk_size):
    yield lst[i:i + chunk_size]

def write_rows(rows, file):
  for row in rows:
    file.write('%s' % row)

part = 1
for chunk in chunks(rest, chunk_size):
  with open('part%d' % part, 'w') as file:
    write_rows(headers, file)
    write_rows(chunk, file)
  part += 1

这是一个测试运行：

$ cat file && python mkt.py && for p in part*; do echo ---- $p; cat $p; done
header
1
2
3
4
5
6
7
8
9
10
11
12
13
14
---- part1
header
1
2
3
4
---- part2
header
5
6
7
8
---- part3
header
9
10
11
12
---- part4
header
13
14

显然，改变chunk_size以及你如何获取headers取决于他们的计数。

Credits:

• https://stackoverflow.com/a/312464/438544

编辑 - 要逐行执行此操作以避免内存问题，您可以执行以下操作：

from itertools import islice

headers_count = 5
chunk_size = 250000

with open('file') as fin:
  headers = list(islice(fin, headers_count))

  part = 1
  while True:
    line_iter = islice(fin, chunk_size)
    try:
      first_line = line_iter.next()
    except StopIteration:
      break
    with open('part%d' % part, 'w') as fout:
      for line in headers:
        fout.write(line)
      fout.write(first_line)
      for line in line_iter:
        fout.write(line)
    part += 1

Credits:

• Python如何一次读取N行

测试用例（将以上内容放入名为mkt2.py):

创建一个包含 5 行标题和 1234567 行的文件：

with open('file', 'w') as fout:
  for i in range(5):
    fout.write(10 * ('header %d ' % i) + '\n')
  for i in range(1234567):
    fout.write(10 * ('line %d ' % i) + '\n')

要测试的 Shell 脚本（放入名为rt.sh):

rm part*
echo ---- file
head -n7 file
tail -n2 file

python mkt2.py

for i in part*; do
  echo ---- $i
  head -n7 $i
  tail -n2 $i
done

示例输出：

$ sh rt.sh 
---- file
header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 
header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 
header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 
header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 
header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 
line 0 line 0 line 0 line 0 line 0 line 0 line 0 line 0 line 0 line 0 
line 1 line 1 line 1 line 1 line 1 line 1 line 1 line 1 line 1 line 1 
line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 
line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 
---- part1
header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 
header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 
header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 
header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 
header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 
line 0 line 0 line 0 line 0 line 0 line 0 line 0 line 0 line 0 line 0 
line 1 line 1 line 1 line 1 line 1 line 1 line 1 line 1 line 1 line 1 
line 249998 line 249998 line 249998 line 249998 line 249998 line 249998 line 249998 line 249998 line 249998 line 249998 
line 249999 line 249999 line 249999 line 249999 line 249999 line 249999 line 249999 line 249999 line 249999 line 249999 
---- part2
header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 
header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 
header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 
header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 
header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 
line 250000 line 250000 line 250000 line 250000 line 250000 line 250000 line 250000 line 250000 line 250000 line 250000 
line 250001 line 250001 line 250001 line 250001 line 250001 line 250001 line 250001 line 250001 line 250001 line 250001 
line 499998 line 499998 line 499998 line 499998 line 499998 line 499998 line 499998 line 499998 line 499998 line 499998 
line 499999 line 499999 line 499999 line 499999 line 499999 line 499999 line 499999 line 499999 line 499999 line 499999 
---- part3
header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 
header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 
header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 
header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 
header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 
line 500000 line 500000 line 500000 line 500000 line 500000 line 500000 line 500000 line 500000 line 500000 line 500000 
line 500001 line 500001 line 500001 line 500001 line 500001 line 500001 line 500001 line 500001 line 500001 line 500001 
line 749998 line 749998 line 749998 line 749998 line 749998 line 749998 line 749998 line 749998 line 749998 line 749998 
line 749999 line 749999 line 749999 line 749999 line 749999 line 749999 line 749999 line 749999 line 749999 line 749999 
---- part4
header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 
header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 
header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 
header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 
header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 
line 750000 line 750000 line 750000 line 750000 line 750000 line 750000 line 750000 line 750000 line 750000 line 750000 
line 750001 line 750001 line 750001 line 750001 line 750001 line 750001 line 750001 line 750001 line 750001 line 750001 
line 999998 line 999998 line 999998 line 999998 line 999998 line 999998 line 999998 line 999998 line 999998 line 999998 
line 999999 line 999999 line 999999 line 999999 line 999999 line 999999 line 999999 line 999999 line 999999 line 999999 
---- part5
header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 header 0 
header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 header 1 
header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 header 2 
header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 header 3 
header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 header 4 
line 1000000 line 1000000 line 1000000 line 1000000 line 1000000 line 1000000 line 1000000 line 1000000 line 1000000 line 1000000 
line 1000001 line 1000001 line 1000001 line 1000001 line 1000001 line 1000001 line 1000001 line 1000001 line 1000001 line 1000001 
line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 line 1234565 
line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 line 1234566 

上述时间安排：

real    0m0.935s
user    0m0.708s
sys     0m0.200s

希望这可以帮助。