蓄水池抽样法

 

 1 #!/usr/bin/env python
 2 # coding=utf-8
 3 
 4 '''
 5 蓄水池抽样法。从不知道总数的样本中随机抽取k个，要求只遍历一次样本。
 6 '''
 7 
 8 import sys
 9 import random
10 
11 if __name__ == '__main__':
12     '''命令行参数：输入文件，抽取多少行，输出文件。输出文件不指定时，默认为输出到控制台'''
13     if len(sys.argv) < 3:
14         print "input [infile] [lines] [outfile=console]"
15     infile = sys.argv[1]
16     k = int(sys.argv[2])
17     if len(sys.argv) >= 4:
18         f_handler = open(sys.argv[3], 'w')
19         sys.stdout = f_handler
20     rect = []
21     lineNo = 0
22     with open(infile, 'r') as f_in:
23         for i in range(k):
24             line = f_in.readline()
25             if line:
26                 lineNo += 1
27                 rect.append(line.strip('\n'))
28             else:
29                 break
30         while True:
31             line = f_in.readline()
32             if not line:
33                 break
34             lineNo += 1
35             rnd = random.randint(1, lineNo + 1)
36             if rnd < k:
37                 rect[rnd] = line.strip('\n')
38     for ele in rect:
39         print ele

 

posted @ 2015-11-01 16:13  张朝阳  阅读(550)  评论(0)  编辑  收藏  举报