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7
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1 #!/usr/bin/env python
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2
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3 """
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4 Sampling random records from a file. Each record is defined by a fixed number of lines.
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5
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6 Usage: sampline.py [options]
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7
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8 Options:
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9 -h, --help show this help message and exit
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10 -r, --replacement Sampling with replacement
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11 -i INPUT, --input=INPUT
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12 Input file
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13 -o OUTPUT, --output=OUTPUT
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14 Output file
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15 -k NSAMPLE, --nSample=NSAMPLE
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16 (required) number of records to be sampled/output
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17 -m RECSIZE, --recSize=RECSIZE
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18 (default=1) number of lines spanned by each record
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19 -n NSKIP, --nSkip=NSKIP
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20 (default=0) number of comment lines to skip at the
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21 beginning
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22
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23 example:
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24 python sampline.py -i test10000.fastq -o out.txt --nSample=5 --recSize=4 --nSkip=0 --replacement
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25 """
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26
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27 import optparse, string, random,sys,math,itertools
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28
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29 assert sys.version_info[:2] >= ( 2, 4 )
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30
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31 def main():
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32
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33 # Parse command line
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34 parser = optparse.OptionParser( usage="%prog [options] " )
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35 parser.add_option( "-r", "--replacement", action="store_true", dest="replacement",default=False,
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36 help="Sampling with replacement" )
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37 parser.add_option( "-i", "--input", dest="input", default=None,
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38 help="Input file" )
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39 parser.add_option( "-o", "--output", dest="output", default=None,
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40 help="Output file" )
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41 parser.add_option("-k","--nSample", type='int',dest="nSample",default=None,
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42 help="(required) number of records to be sampled/output" )
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43 parser.add_option("-m","--recSize", type='int',dest="recSize",default=1,
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44 help="(default=1) number of lines spanned by each record" )
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45 parser.add_option("-n","--nSkip", type='int',dest="nSkip",default=0,
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46 help="(default=0) number of comment lines to skip at the beginning")
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47 options, args = parser.parse_args()
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48 #assert options.region in ( 'coding', 'utr3', 'utr5', 'transcribed' ), "Invalid region argument"
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49
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50 sampline(options.input,options.output,options.nSample,options.recSize,options.nSkip,options.replacement)
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51
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52 def sample_wr(population, k):
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53 "Chooses k random elements (with replacement) from a population"
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54 n = len(population)
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55 _random, _int = random.random, int # speed hack
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56 return [_int(_random() * n) for i in itertools.repeat(None, k)]
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57
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58 # num of lines
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59 def readinput(filename):
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60 try:
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61 f = open (filename)
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62 except:
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63 print >> sys.stderr, "can't open file "+str(filename)
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64 sys.exit(0)
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65
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66 nline = 0
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67 for line in f:
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68 nline = nline + 1
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69 f.close()
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70 return nline
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71
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72 def sampline(infile,outfile,nSample,recSize,nSkip,replacement):
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73 # sample nSample records from file
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74 # each record contains recSize lines
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75 # skip the top nSkip lines
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76
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77 nLine = readinput(infile)
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78 print 'num of lines in input: ',nLine
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79 print 'avoid sampling the first ',nSkip,' lines'
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80 print 'lines per record: ',recSize
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81
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82 if (nLine-nSkip) % recSize:
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83 print >> sys.stderr, "the number of lines is not dividable by record size!"
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84 sys.exit(0)
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85
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86 nTotalRecords = (nLine-nSkip) / recSize
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87 print "total number of records: ",nTotalRecords
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88
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89 if replacement or nTotalRecords < nSample:
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90 sel = sample_wr(range(nTotalRecords),nSample)
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91 else:
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92 sel = random.sample(range(nTotalRecords),nSample)
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93
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94 #print len(sel), sorted(sel)
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95
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96 # output
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97 try:
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98 fout = open (outfile,'w')
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99 except:
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100 print >> sys.stderr, "can't open file "+str(outfile)
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101 sys.exit(0)
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102 fin = open(infile)
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103 n = 0 # index of line
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104 rec = "" # to store all content of a record
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105 nrepeat = 0 # number of times a record is sampled
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106 curr_rec = -1
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107 for line in fin:
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108 if n < nSkip:
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109 n = n + 1
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110 fout.write(line)
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111 continue
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112
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113 if not (n-nSkip) % recSize:# a new record
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114 # print the previous sampled record
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115 for i in range(nrepeat):
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116 fout.write(rec)
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117 curr_rec = (n-nSkip)/recSize
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118 nrepeat = sel.count(curr_rec)
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119 if nrepeat: # sampled
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120 rec = line
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121 #print curr_rec,nrepeat
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122 elif (n-nSkip)/recSize == curr_rec:
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123 rec = rec + line
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124 n = n + 1
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125 # if the last record is selected
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126 if curr_rec == nTotalRecords-1:
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127 for i in range(nrepeat):
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128 fout.write(rec)
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129 fin.close()
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130 fout.close()
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131
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132
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133 if __name__ == "__main__": main()
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