subset.py
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1 #!/usr/bin/env python
2 
3 import os, sys, math, random
4 from collections import defaultdict
5 
6 if sys.version_info[0] >= 3:
7  xrange = range
8 
9 def exit_with_help(argv):
10  print("""\
11 Usage: {0} [options] dataset subset_size [output1] [output2]
12 
13 This script randomly selects a subset of the dataset.
14 
15 options:
16 -s method : method of selection (default 0)
17  0 -- stratified selection (classification only)
18  1 -- random selection
19 
20 output1 : the subset (optional)
21 output2 : rest of the data (optional)
22 If output1 is omitted, the subset will be printed on the screen.""".format(argv[0]))
23  exit(1)
24 
25 def process_options(argv):
26  argc = len(argv)
27  if argc < 3:
28  exit_with_help(argv)
29 
30  # default method is stratified selection
31  method = 0
32  subset_file = sys.stdout
33  rest_file = None
34 
35  i = 1
36  while i < argc:
37  if argv[i][0] != "-":
38  break
39  if argv[i] == "-s":
40  i = i + 1
41  method = int(argv[i])
42  if method not in [0,1]:
43  print("Unknown selection method {0}".format(method))
44  exit_with_help(argv)
45  i = i + 1
46 
47  dataset = argv[i]
48  subset_size = int(argv[i+1])
49  if i+2 < argc:
50  subset_file = open(argv[i+2],'w')
51  if i+3 < argc:
52  rest_file = open(argv[i+3],'w')
53 
54  return dataset, subset_size, method, subset_file, rest_file
55 
56 def random_selection(dataset, subset_size):
57  l = sum(1 for line in open(dataset,'r'))
58  return sorted(random.sample(xrange(l), subset_size))
59 
60 def stratified_selection(dataset, subset_size):
61  labels = [line.split(None,1)[0] for line in open(dataset)]
62  label_linenums = defaultdict(list)
63  for i, label in enumerate(labels):
64  label_linenums[label] += [i]
65 
66  l = len(labels)
67  remaining = subset_size
68  ret = []
69 
70  # classes with fewer data are sampled first; otherwise
71  # some rare classes may not be selected
72  for label in sorted(label_linenums, key=lambda x: len(label_linenums[x])):
73  linenums = label_linenums[label]
74  label_size = len(linenums)
75  # at least one instance per class
76  s = int(min(remaining, max(1, math.ceil(label_size*(float(subset_size)/l)))))
77  if s == 0:
78  sys.stderr.write('''\
79 Error: failed to have at least one instance per class
80  1. You may have regression data.
81  2. Your classification data is unbalanced or too small.
82 Please use -s 1.
83 ''')
84  sys.exit(-1)
85  remaining -= s
86  ret += [linenums[i] for i in random.sample(xrange(label_size), s)]
87  return sorted(ret)
88 
89 def main(argv=sys.argv):
90  dataset, subset_size, method, subset_file, rest_file = process_options(argv)
91  #uncomment the following line to fix the random seed
92  #random.seed(0)
93  selected_lines = []
94 
95  if method == 0:
96  selected_lines = stratified_selection(dataset, subset_size)
97  elif method == 1:
98  selected_lines = random_selection(dataset, subset_size)
99 
100  #select instances based on selected_lines
101  dataset = open(dataset,'r')
102  prev_selected_linenum = -1
103  for i in xrange(len(selected_lines)):
104  for cnt in xrange(selected_lines[i]-prev_selected_linenum-1):
105  line = dataset.readline()
106  if rest_file:
107  rest_file.write(line)
108  subset_file.write(dataset.readline())
109  prev_selected_linenum = selected_lines[i]
110  subset_file.close()
111 
112  if rest_file:
113  for line in dataset:
114  rest_file.write(line)
115  rest_file.close()
116  dataset.close()
117 
118 if __name__ == '__main__':
119  main(sys.argv)
120 
def process_options(argv)
Definition: subset.py:25
#define max(x, y)
Definition: libsvmread.c:15
def stratified_selection(dataset, subset_size)
Definition: subset.py:60
xrange
Definition: subset.py:7
def random_selection(dataset, subset_size)
Definition: subset.py:56
def exit_with_help(argv)
Definition: subset.py:9
#define min(x, y)
Definition: libsvmread.c:18
def main(argv=sys.argv)
Definition: subset.py:89


ml_classifiers
Author(s): Scott Niekum , Joshua Whitley
autogenerated on Mon Feb 28 2022 22:46:49