How do I create a list of random numbers without duplicates

Question

I tried using random randint 0  100   but some numbers were the same  Is there a method module to create a list unique random numbers   Note  The following code is based on an answer and has been added after the answer was posted  It is not a part of the question  it is the solution   def getScores          open files to read and write     f1   open  page txt    r        p1   open  pgRes txt    a         gScores           bScores           yScores              run 50 tests of 40 random queries to implement  bootstrapping  method      for i in range 50             get 40 random queries from the 50         lines   random sample f1 readlines    40

User · Answer

If you wish to ensure that the numbers being added are unique, you could use a Set object

if using 2.7 or greater, or import the sets module if not.

As others have mentioned, this means the numbers are not truly random.

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The solution presented in this answer works  but it could become problematic with memory if the sample size is small  but the population is huge  e g  random sample insanelyLargeNumber  10      To fix that  I would go with this   answer   set   sampleSize   10 answerSize   0  while answerSize  lt  sampleSize      r   random randint 0 100      if r not in answer          answerSize    1         answer add r     answer now contains 10 unique  random integers from 0   100

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The answer provided here works very well with respect to time as well as memory but a bit more complicated as it uses advanced python constructs such as yield  The simpler answer works well in practice but  the issue with that  answer is that it may generate many spurious integers before actually constructing the required set  Try it out with populationSize   1000  sampleSize   999  In theory  there is a chance that it doesn t terminate   The answer below addresses both issues  as it is deterministic and somewhat efficient though currently not as efficient as the other two   def randomSample populationSize  sampleSize     populationStr   str populationSize    dTree  samples            for i in range sampleSize       val  dTree   getElem populationStr  dTree          samples append int val     return samples  dTree   where the functions getElem  percolateUp are as defined below  import random  def getElem populationStr  dTree  key     msd    int populationStr 0     if not key in dTree keys        dTree key    range msd   1    idx   random randint 0  len dTree key   - 1    key   key    str dTree key  idx     if len populationStr     1      dTree key  -1   pop idx      return key   percolateUp dTree  key  -1      newPopulation   populationStr 1     if int key -1      msd      newPopulation   str 10   len newPopulation   - 1    return getElem newPopulation  dTree  key   def percolateUp dTree  key     while  dTree key              dTree key  -1   remove  int key -1         key   key  -1    return dTree   Finally  the timing on average was about 15ms for a large value of n as shown below   In  3   n   10000000000000000000000000000000  In  4    time l t   randomSample n  5  Wall time  15 ms  In  5   l Out 5    10000000000000000000000000000000L   5731058186417515132221063394952L   85813091721736310254927217189L   6349042316505875821781301073204L   2356846126709988590164624736328L

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This will return a list of 10 numbers selected from the range 0 to 99  without duplicates   import random random sample range 100   10    With reference to your specific code example  you probably want to read all the lines from the file once and then select random lines from the saved list in memory  For example   all lines   f1 readlines   for i in range 50       lines   random sample all lines  40    This way  you only need to actually read from the file once  before your loop  It s much more efficient to do this than to seek back to the start of the file and call f1 readlines   again for each loop iteration

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Here is a very small function I made  hope this helps  import random numbers   list range 0  100   random shuffle numbers

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import random  sourcelist    resultlist     for x in range 100       sourcelist append x   for y in sourcelist      resultlist insert random randint 0 len resultlist   y   print  resultlist

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You can use the shuffle function from the random module like this   import random  my list   list xrange 1 100     list of integers from 1 to 99                                 adjust this boundaries to fit your needs random shuffle my list  print my list    lt - List of unique random numbers   Note here that the shuffle method doesn t return any list as one may expect  it only shuffle the list passed by reference

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A very simple function that also solves your problem  from random import randint  data       def unique rand inicial  limit  total            data               i   0          while i  lt  total              number   randint inicial  limit              if number not in data                  data append number                  i    1          return data   data   unique rand 1  60  6   print data         prints something like    34  45  2  36  25  32

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If the list of N numbers from 1 to N is randomly generated  then yes  there is a possibility that some numbers may be repeated   If you want a list of numbers from 1 to N in a random order  fill an array with integers from 1 to N  and then use a Fisher-Yates shuffle or Python s random shuffle

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Linear Congruential Pseudo-random Number Generator  O 1  Memory O k  Operations  This problem can be solved with a simple Linear Congruential Generator  This requires constant memory overhead  8 integers  and at most 2  sequence length  computations  All other solutions use more memory and more compute  If you only need a few random sequences  this method will be significantly cheaper  For ranges of size N  if you want to generate on the order of N unique k-sequences or more  I recommend the accepted solution using the builtin methods random sample range N  k  as this has been optimized in python for speed  Code   Return a randomized  quot range quot  using a Linear Congruential Generator   to produce the number sequence  Parameters are the same as for    python builtin  quot range quot       Memory  -- storage for 8 integers  regardless of parameters      Compute -- at most 2  quot maximum quot  steps required to generate sequence    def random range start  stop None  step None       import random  math       Set a default values the same way  quot range quot  does      if  stop    None   start  stop   0  start     if  step    None   step   1       Use a mapping to convert a standard range into the desired range      mapping   lambda i   i step    start       Compute the number of numbers in this range      maximum    stop - start     step       Seed range with a random integer      value   random randint 0 maximum               Construct an offset  multiplier  and modulus for a linear       congruential generator  These generators are cyclic and       non-repeating when they maintain the properties                 1   quot modulus quot  and  quot offset quot  are relatively prime          2    quot multiplier quot  - 1  is divisible by all prime factors of  quot modulus quot           3    quot multiplier quot  - 1  is divisible by 4 if  quot modulus quot  is divisible by 4             offset   random randint 0 maximum    2   1        Pick a random odd-valued offset      multiplier   4  maximum  4    1                   Pick a multiplier 1 greater than a multiple of 4      modulus   int 2  math ceil math log2 maximum      Pick a modulus just big enough to generate all numbers  power of 2         Track how many random numbers have been returned      found   0     while found  lt  maximum            If this is a valid value  yield it in generator fashion          if value  lt  maximum              found    1             yield mapping value            Calculate the next value in the sequence          value    value multiplier   offset    modulus  Usage The usage of this function  quot random range quot  is the same as for any generator  like  quot range quot    An example    Show off random range  print   for v in range 3 6       v   2  v     l   list random range v       print  quot Need quot  v  quot found quot  len set l    quot  min max  quot   min l  max l        print  quot  quot  l      print    Sample Results Required 8 cycles to generate a sequence of 8 values  Need 8 found 8  min max   0  7    1  0  7  6  5  4  3  2   Required 16 cycles to generate a sequence of 9 values  Need 9 found 9  min max   0  8    3  5  8  7  2  6  0  1  4   Required 16 cycles to generate a sequence of 16 values  Need 16 found 16  min max   0  15    5  14  11  8  3  2  13  1  0  6  9  4  7  12  10  15   Required 32 cycles to generate a sequence of 17 values  Need 17 found 17  min max   0  16    12  6  16  15  10  3  14  5  11  13  0  1  4  8  7  2        Required 32 cycles to generate a sequence of 32 values  Need 32 found 32  min max   0  31    19  15  1  6  10  7  0  28  23  24  31  17  22  20  9        Required 64 cycles to generate a sequence of 33 values  Need 33 found 33  min max   0  32    11  13  0  8  2  9  27  6  29  16  15  10  3  14  5  24

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You can first create a list of numbers from a to b  where a and b are respectively the smallest and greatest numbers in your list  then shuffle it with Fisher-Yates algorithm or using the Python s random shuffle method

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From the CLI in win xp    python -c  import random  print sorted set  random randint 6 49  for i in range 7      6      In Canada we have the 6 49 Lotto  I just wrap the above code in lotto bat and run C  home lotto bat or just C  home lotto   Because random randint often repeats a number  I use set with range 7  and then shorten it to a length of 6   Occasionally if a number repeats more than 2 times the resulting list length will be less than 6   EDIT  However  random sample range 6 49  6  is the correct way to go

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You can use Numpy library for quick answer as shown below -  Given code snippet lists down 6 unique numbers between the range of 0 to 5  You can adjust the parameters for your comfort   import numpy as np import random a   np linspace  0  5  6   random shuffle a  print a    Output    2   1   5   3   4   0     It doesn t put any constraints as we see in random sample as referred here   Hope this helps a bit

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import random result    for i in range 1 50       rng random randint 1 20      result append rng

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The problem with the set based approaches   if random value in return values  try again   is that their runtime is undetermined due to collisions  which require another  try again  iteration   especially when a large amount of random values are returned from the range   An alternative that isn t prone to this non-deterministic runtime is the following   import bisect import random  def fast sample low  high  num           Samples  param num  integer numbers in range of           param low    param high   without replacement         by maintaining a list of ranges of values that         are permitted           This list of ranges is used to map a random number         of a contiguous a range   r n   to a permissible         number  r   from  ranges                ranges    high      high    high - 1     while len ranges  - 1  lt  num            generate a random number from an ever decreasing           contiguous range  which we ll map to the true           random number             consider an example with low 0  high 10            part way through this loop with                      ranges    0  2  3  7  9  10                      r n  - gt  r             0  - gt  1             1  - gt  4             2  - gt  5             3  - gt  6             4  - gt  8         r n   random randint low  high           range index   bisect bisect left ranges  r n          r   r n   range index         for i in xrange range index  len ranges                if ranges i   lt   r                    as many  gaps  we iterate over  as much                   is the true random value   r   shifted                  r   r n   i   1             elif ranges i   gt  r n                  break           mark  r  as another  gap  of the original            low  high  range          ranges insert i  r            Fewer values possible          high  -  1        ranges  happens to contain the result      return ranges  -1

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In order to obtain a program that generates a list of random values without duplicates that is deterministic  efficient and built with basic programming constructs consider the function extractSamples defined below  def extractSamples populationSize  sampleSize  intervalLst        import random     if  sampleSize  gt  populationSize            raise ValueError  quot sampleSize    quot  str sampleSize    quot   gt  populationSize     quot    str populationSize     quot   quot       samples          while  len samples   lt  sampleSize            i   random randint 0   len intervalLst -1            a b    intervalLst i          sample   random randint a b          if  a  b                intervalLst pop i          elif  a    sample      shorten beginning of interval                                                                                                                                                        intervalLst i     sample 1  b          elif   sample    b      shorten interval end                                                                                                                                                                intervalLst i     a  sample - 1          else               intervalLst i     a  sample - 1              intervalLst append  sample 1  b           samples append sample      return samples  The basic idea is to keep track of intervals intervalLst for possible values from which to select our required elements from  This is deterministic in the sense that we are guaranteed to generate a sample within a fixed number of steps  solely dependent on populationSize and sampleSize   To use the above function to generate our required list  In  3   populationSize  sampleSize   10  17  10  5  In  4    time lst1   extractSamples populationSize  sampleSize    0  populationSize-1    CPU times  user 289 ms  sys  9 96 ms  total  299 ms Wall time  293 ms   We may also compare with an earlier solution  for a lower value of populationSize  In  5   populationSize  sampleSize   10  8  10  5  In  6    time lst   random sample range populationSize   sampleSize  CPU times  user 1 89 s  sys  299 ms  total  2 19 s Wall time  2 18 s  In  7    time lst1   extractSamples populationSize  sampleSize    0  populationSize-1    CPU times  user 449 ms  sys  8 92 ms  total  458 ms Wall time  442 ms  Note that I reduced populationSize value as it produces Memory Error for higher values when using the random sample solution  also mentioned in previous answers here and here   For above values  we can also observe that extractSamples outperforms the random sample approach  P S    Though the core approach is similar to my earlier answer  there are substantial modifications in implementation as well as approach alongwith improvement in clarity

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to sample integers without replacement between minval and maxval   import numpy as np  minval  maxval  n samples   -50  50  10 generator   np random default rng seed 0  samples   generator permutation np arange minval  maxval    n samples     or  if minval is 0  samples   generator permutation maxval   n samples    with jax   import jax  minval  maxval  n samples   -50  50  10 key   jax random PRNGKey seed 0  samples   jax random shuffle key  jax numpy arange minval  maxval    n samples

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If you need to sample extremely large numbers  you cannot use range   random sample range 10000000000000000000000000000000   10    because it throws   OverflowError  Python int too large to convert to C ssize t   Also  if random sample cannot produce the number of items you want due to the range being too small   random sample range 2   1000    it throws    ValueError  Sample larger than population   This function resolves both problems   import random  def random sample count  start  stop  step 1       def gen random            while True              yield random randrange start  stop  step       def gen n unique source  n           seen   set           seenadd   seen add         for i in  i for i in source   if i not in seen and not seenadd i                yield i             if len seen     n                  break      return  i for i in gen n unique gen random                                      min count  int abs stop - start    abs step        Usage with extremely large numbers   print   n  join map str  random sample 10  2  10000000000000000000000000000000       Sample result   7822019936001013053229712669368 6289033704329783896566642145909 2473484300603494430244265004275 5842266362922067540967510912174 6775107889200427514968714189847 9674137095837778645652621150351 9969632214348349234653730196586 1397846105816635294077965449171 3911263633583030536971422042360 9864578596169364050929858013943   Usage where the range is smaller than the number of requested items   print      join map str  random sample 100000  0  3       Sample result   2  0  1   It also works with with negative ranges and steps   print      join map str  random sample 10  10  -10  -2     print      join map str  random sample 10  5  -5  -2       Sample results   2  -8  6  -2  -4  0  4  10  -6  8 -3  1  5  -1  3

[python] How do I create a list of random numbers without duplicates?

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