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1 #!/usr/bin/env python
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2 # Kanwei Li, 2010
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3 # Selects N random lines from a file and outputs to another file
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4
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5 import random, sys
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6
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7 def main():
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8 infile = open(sys.argv[1], 'r')
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9 total_lines = int(sys.argv[2])
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10
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11 if total_lines < 1:
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12 sys.stderr.write( "Must select at least one line." )
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13 sys.exit()
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14
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15 kept = []
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16 n = 0
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17 for line in infile:
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18 line = line.rstrip("\n")
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19 n += 1
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20 if (n <= total_lines):
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21 kept.append(line)
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22 elif random.randint(1, n) <= total_lines:
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23 kept.pop(random.randint(0, total_lines-1))
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24 kept.append(line)
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25
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26 if n < total_lines:
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27 sys.stderr.write( "Error: asked to select more lines than there were in the file." )
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28 sys.exit()
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29
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30 open(sys.argv[3], 'w').write( "\n".join(kept) )
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31
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32 if __name__ == "__main__":
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33 main()
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