Generating UNIQUE Random Numbers within a range

Question

I need to generate random UNIQUE numbers within a range  how can I do that  I can generate random number by generator   arr        x   rand  min   max    len   count  arr    flag   0  for  i   0   i  lt   len   i       if   flag     1     goto generator   if   x      arr  i       flag   1     arr  index     x   index     goto generator   I know this code is bad  so I need a better optimized code of my version   help   example  if i need to generate 3 numbers within 1 to 15 they should be like 5  9  1 but not 3 1 2  with in 1 - 3  numbers i want to generate

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The  shuffle  method has a MAJOR FALW  When the numbers are big  shuffle 3 billion indexs will instantly CAUSE 500 error  Here comes a best solution for really big numbers   function getRandomNumbers  min   max   total         temp arr   array        while sizeof  temp arr   lt   total   temp arr rand  min   max     true      return  temp arr      Say I want to get 10 unique random numbers from 1 billion to 4 billion    random numbers   getRandomNumbers 1000000000 4000000000 10     PS  Execution time  0 027 microseconds

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If you need 5 random numbers between 1 and 15  you should do   var dump getRandomNumbers 1  15  5     function getRandomNumbers  min   max   count        if   count  gt     max -  min  1                 return false             values   range  min   max       shuffle  values       return array slice  values 0   count       It will return false if you specify a count value larger then the possible range of numbers

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The idea consists to use the keys  when a value is already present in the array keys  the array size stays the same   function getDistinctRandomNumbers   nb   min   max        if   max -  min   1  lt   nb          return false     or throw an exception       res   array        do            res mt rand  min   max     1        while  count  res       nb       return array keys  res        Pro  This way avoids the use of in array and doesn t generate a huge array  So  it is fast and preserves a lot of memory   Cons  when the rate  range quantity  decreases  the speed decreases too  but stays correct   For a same rate  relative speed increases with the range size          I understand that fact since there are more free integers to select  in particular for the first steps   but if somebody has the mathematical formula that describes this behaviour  I am interested by  don t hesitate   Conclusion  The best  general  function seems to be a mix between this function and  Anne function that is more efficient with a little rate  This function should switch between the two ways when a certain quantity is needed and a rate  range quantity  is reached  So the complexity time of the test to know that  must be taken in account

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Get a random number  Is it stored in the array already  If not  store it  If so  then go get another random number and repeat

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I guess this is probably a non issue for most but I tried to solve it   I think I have a pretty decent solution  In case anyone else stumbles upon this issue   function randomNums  gen   trim   low   high         results to gen    gen       low range         low       high range        high       trim results to   trim        items   array         results   range  1   results to gen        i   1       foreach  results as  result                 result   mt rand   low range   high range            items      result                unique   array unique   items  SORT NUMERIC        countem   count   unique        unique counted    countem - trim results to        sum   array slice  unique   unique counted         foreach   sum as  key                 output    i          key   lt br gt            echo  output             randomNums 1100  1000  890000  899999

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Array with range of numbers at random order    numbers   range 1  20   shuffle  numbers     Wrapped function   function UniqueRandomNumbersWithinRange  min   max   quantity         numbers   range  min   max       shuffle  numbers       return array slice  numbers  0   quantity       Example    lt  php print r  UniqueRandomNumbersWithinRange 0 25 5       gt    Result    Array        0    gt  14      1    gt  16      2    gt  17      3    gt  20      4    gt  1

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This probably will solve your problem    lt  php print r array rand range 1 50   5      gt

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When creating an application where I needed to generate 30 000 unique numbers within a larger range  I was able to cut down processing time from 25 seconds to 1 5 seconds using this method   The idea is that PHP is much faster at generating random numbers than it is at checking the existence of items in an array - that is why using a while in array  loop can be slow    count   0   collectNumbers       while   count  lt  30000    for   i   0   i  lt  60000   i        rand   mt rand 1  100000    collectNumbers      rand      unique   array unique  collectNumbers    count   count  unique       finalArray   array slice  unique  0  30000     This will return 30 000 unique numbers extremely quickly  Using an iteration value that is double the amount of numbers you need to generate can increase the likelihood of unique numbers the first iteration    but regardless of how many iterations it takes  this will produce a result faster than checking your array for repeated numbers in a loop

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Simply use this function and pass the count of number you want to generate  Code   function randomFix  length         random       srand  double microtime   1000000     data    AbcDE123IJKLMN67QRSTUVWXYZ    data     aBCdefghijklmn123opq45rs67tuv89wxyz    data     0FGH45OP89    for  i   0   i  lt   length   i           random    substr  data   rand    strlen  data     1     return  random

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You can try next code   function unique randoms  min   max   count       arr   array     while count  arr   lt   count          tmp  mt rand  min  max         if  in array  tmp   arr              arr      tmp             return  arr

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len   10       total number of numbers  min   100      minimum  max   999      maximum  range          initialize array foreach  range 0   len - 1  as  i        while in array  num   mt rand  min   max    range         range      num    print r  range       I was interested to see how the accepted answer stacks up against mine  It s useful to note  a hybrid of both may be advantageous  in fact a function that conditionally uses one or the other depending on certain values     The accepted answer function randRange1  min   max   count         numbers   range  min   max       shuffle  numbers       return array slice  numbers  0   count        My answer function randRange2  min   max   count         range   array        while   i    lt   count            while in array  num   mt rand  min   max    range             range      num            return  range     echo  randRange1  small range  high count    PHP EOL   time   microtime true   randRange1 0  9999  5000   echo  microtime true  -  time    PHP EOL   PHP EOL   echo  randRange2  small range  high count    PHP EOL   time   microtime true   randRange2 0  9999  5000   echo  microtime true  -  time    PHP EOL   PHP EOL   echo  randRange1  high range  small count    PHP EOL   time   microtime true   randRange1 0  999999  6   echo  microtime true  -  time    PHP EOL   PHP EOL   echo  randRange2  high range  small count    PHP EOL   time   microtime true   randRange2 0  999999  6   echo  microtime true  -  time    PHP EOL   PHP EOL    The results   randRange1  small range  high count 0 019910097122192  randRange2  small range  high count 1 5043621063232  randRange1  high range  small count 2 4722430706024  randRange2  high range  small count 0 0001051425933837   If you re using a smaller range and a higher count of returned values  the accepted answer is certainly optimal  however as I had expected  larger ranges and smaller counts will take much longer with the accepted answer  as it must store every possible value in range  You even run the risk of blowing PHP s memory cap  A hybrid that evaluates the ratio between range and count  and conditionally chooses the generator would be the best of both worlds

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This is how I would do it    randnum1   mt rand 1 20     nomatch   0   while  nomatch    0     randnum2   mt rand 1 20    if  randnum2     randnum1     nomatch   1          nomatch   0   while  nomatch    0     randnum3   mt rand 1 20    if   randnum3     randnum1 and  randnum3     randnum2      nomatch   1          Then you can echo the results to check  echo  Random numbers are      randnum1          randnum2      and      randnum3     n

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If you want to generate 100 numbers that are random  but each number appearing only once  a good way would be to generate an array with the numbers in order  then shuffle it   Something like this    arr   array     for   i 1  i lt  101  i           arr      i     shuffle  arr    print r  arr     Output will look something like this   Array        0    gt  16      1    gt  93      2    gt  46      3    gt  55      4    gt  18      5    gt  63      6    gt  19      7    gt  91      8    gt  99      9    gt  14      10    gt  45      11    gt  68      12    gt  61      13    gt  86      14    gt  64      15    gt  17      16    gt  27      17    gt  35      18    gt  87      19    gt  10      20    gt  95      21    gt  43      22    gt  51      23    gt  92      24    gt  22      25    gt  58      26    gt  71      27    gt  13      28    gt  66      29    gt  53      30    gt  49      31    gt  78      32    gt  69      33    gt  1      34    gt  42      35    gt  47      36    gt  26      37    gt  76      38    gt  70      39    gt  100      40    gt  57      41    gt  2      42    gt  23      43    gt  15      44    gt  96      45    gt  48      46    gt  29      47    gt  81      48    gt  4      49    gt  33      50    gt  79      51    gt  84      52    gt  80      53    gt  101      54    gt  88      55    gt  90      56    gt  56      57    gt  62      58    gt  65      59    gt  38      60    gt  67      61    gt  74      62    gt  37      63    gt  60      64    gt  21      65    gt  89      66    gt  3      67    gt  32      68    gt  25      69    gt  52      70    gt  50      71    gt  20      72    gt  12      73    gt  7      74    gt  54      75    gt  36      76    gt  28      77    gt  97      78    gt  94      79    gt  41      80    gt  72      81    gt  40      82    gt  83      83    gt  30      84    gt  34      85    gt  39      86    gt  6      87    gt  98      88    gt  8      89    gt  24      90    gt  5      91    gt  11      92    gt  73      93    gt  44      94    gt  85      95    gt  82      96    gt  75      97    gt  31      98    gt  77      99    gt  9      100    gt  59

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The best way to generate the unique random number is    lt  php      echo md5 uniqid mt rand    true  microtime true      gt

[php] Generating UNIQUE Random Numbers within a range

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