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 < $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) ]

Unique random number? "Unique number" and "random number" cannot coexist. Think about it. You can have unique. Or you can have random. Which do you want? — Pete Wilson, Apr 10 '11 at 15:13
i want random number and store it in array, all the number in the array must be unique — Sourav, Apr 10 '11 at 15:14
Are those `goto` statements? I feel like I'm reading `TI-BASIC`... — Blender, Apr 10 '11 at 15:16
@Soulav I updated my answer, you might be interested to give it a read. — Dan Lugg, Apr 10 '11 at 18:01
@Sourav Actually, PHP only recently introduced `goto` in version 5.3. — Wiseguy, Apr 17 '11 at 04:16

score 144 · Accepted Answer · edited Jan 13 '14 at 18:01

144

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:

<?php
print_r( UniqueRandomNumbersWithinRange(0,25,5) );
?>

Result:

 Array
(
    [0] => 14
    [1] => 16
    [2] => 17
    [3] => 20
    [4] => 1
)

edited Jan 13 '14 at 18:01

Eduard

3,395
8
37
62

answered Apr 10 '11 at 15:19

Anne

26,765
9
65
71

1

This will include *all* numbers within that range, not random ones. – Blender Apr 10 '11 at 15:23
8

If you only need 5 random numbers, just pick the first 5 items in the array. – Anne Apr 10 '11 at 15:25
Good point. Make it into a function and submit it to be included into the massive PHP function database ;) – Blender Apr 10 '11 at 15:26
if i try to generate 3 number with your function they are like 1, 3, 2 but i want something like 1, 5, 15 [if limit is 1-15 ] – Sourav Apr 10 '11 at 15:36
2

Huh? `UniqueRandomNumbersWithinRange(1,15,3)` perfectly returns `( [0] => 13 [1] => 20 [2] => 15 )`. – Anne Apr 10 '11 at 15:42
18

Not a good choice if you want high random numbers. Think how long does it take for this function to generate 30 rand numbers between 1 and 50k. It will first create an array with 50 thousand integers, then will try and shuffle each and every one of them, and then will start slicing from another 50 thousand. – Eduard Jul 11 '13 at 12:14
In PHP 7.1, shuffle() is the culprit here. Not array_slice() or range(). – Bell Dec 15 '16 at 01:57

Dan Lugg · Answer 2 · 2022-12-12T03:42:45.690

$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)
{
    $i = 0;
    $range = array();
    while ($i++ < $count) {
        while(in_array($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.

i really appreciate your code, it executes muchhhh faster than the selected ans, but fails for a little range [1-1000] ! — Sourav, Apr 11 '11 at 07:12
You have a typo: name of the last result is not `randRange1` but `randRange2`. — Jasom Dotnet, Dec 24 '15 at 03:03
If so, we can combine both answers and make an if condition based on the range and count. If anyone can check the best value for the range and count threshold it will be perfect — HendraWD, Apr 28 '17 at 09:08
I got Warning: in_array() expects parameter 2 to be array on line 5 — Adrian P., Jun 30 '17 at 21:46
@AdrianP. You need to initialize `$range` in the initial code snippet, which I never did for some reason; editing. — Dan Lugg, Jun 30 '17 at 21:49
Nice solution for randRange2, but you forgot to add: $i = 0; at the start of the function. — hdries, Dec 07 '22 at 09:54

Casimir et Hippolyte · Answer 3 · 2016-12-15T09:42:56.943

6

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 < $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.

edited Dec 15 '16 at 09:42

answered Jan 26 '15 at 16:31

Casimir et Hippolyte

88,009
5
94
125

@Bell: thanks for your correction, I had indeed missed this. – Casimir et Hippolyte Dec 15 '16 at 09:43
This one needs the upvotes! I posted something similar when I had the thread sorted by votes. `!==$nb` is a nice performance trick. You might want to add `$nb=(int)$nb` in the first line and cast `$min` and `$max` to int as well, just to make sure. – Titus Apr 22 '17 at 01:56
CMIIW, but i think it can generate the same key that has been set previously, so it is unreliable and can lead to too long runtime if `$nb` value is very big and near with `$max - $min` – HendraWD Apr 28 '17 at 08:58
@HendraWD: you are wrong but in a particular way: there's no reason to use this function when for example you want 999.999 random values between 0 and 1.000.000 (it's easier to remove 2 numbers in a shuffled range). Whatever, for the values you are speaking about, I think that none of the solutions here aren't really appropriate for a basic reason: Who wants to end with an array of a million of items or more? In these cases, using a generator function and a "lazy evaluation" strategy is a more proper way. – Casimir et Hippolyte Apr 28 '17 at 15:24
@HendraWD: Note that I already described the phenomenon in the "cons" part of my answer and suggested a way to solve it. – Casimir et Hippolyte Apr 28 '17 at 15:29
I mean `mt_rand($min, $max)` can also generate the same number. While it is the same number, the loop is useless – HendraWD Apr 28 '17 at 15:29
@HendraWD: obviously, and I know that, but despite of these "useless loops" (for reasonable values), it stays very efficient. – Casimir et Hippolyte Apr 28 '17 at 15:33
Yes, but just imagine the condition if the `$max` and `$min` difference is big and `$nb` also big enough, there will be so much useless loops there – HendraWD Apr 28 '17 at 15:35
@HendraWD: I already answered that in my answer and in my previous comment, read them. – Casimir et Hippolyte Apr 28 '17 at 15:37
OK, thank you for your explanation @CasimiretHippolyte – HendraWD Apr 28 '17 at 15:40
The function's performance is really depend on two indexes; `($max - $min) / $count` and smallness of the `$count` itself: it becomes really fast when they increases (as I saw in the tests, from a hundred times to a million times faster than the `shuffle()` way!), but becomes really inefficient when it decreases (sorry to say, but the performance sucks the index reaches 1). – MAChitgarha Jul 10 '19 at 16:58
@MAChitgarha: it isn't a real problem because when `($max - $min)/$count` decreases, all you have to do is to use the same function to select the numbers to exclude from the range. (in other words `$count = $max - $min - $count`) – Casimir et Hippolyte Jul 10 '19 at 17:06
@CasimiretHippolyte Sorry, I didn't understand what you've said. However, your solution works really better than the `shuffle()` way in nearly all cases. The advantage of using this method over that one is that the performance really depends on `$count`, but using `shuffle()`, you would waste your resources because it highly depends on `$max`, even if your `$count` is less than 10. Nevertheless, thanks for posting this answer! ;) – MAChitgarha Jul 10 '19 at 17:16
@MAChitgarha: I mean: instead of selecting 999 random numbers in a range of 1000 numbers, select 1 number and remove it from the range. – Casimir et Hippolyte Jul 10 '19 at 17:20
@CasimiretHippolyte Yes, actually; but I'm considering the other cases. For example, if you want to select 10^5 numbers from 10^6 numbers. Again, as I said, even in these cases, it performs really better than other methods. – MAChitgarha Jul 10 '19 at 17:23

score 3 · Answer 4 · answered Jun 30 '14 at 15:26

3

You can try next code:

function unique_randoms($min, $max, $count) {

 $arr = array();
 while(count($arr) < $count){
      $tmp =mt_rand($min,$max);
      if(!in_array($tmp, $arr)){
         $arr[] = $tmp;
      }
 }
return $arr;
}

answered Jun 30 '14 at 15:26

Brotheryura

1,158
13
21

Gazler · Answer 5 · 2011-04-10T15:45:26.753

3

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 > (($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.

edited Apr 10 '11 at 15:45

answered Apr 10 '11 at 15:17

Gazler

83,029
18
279
245

Note, this is if you don't want all the numbers in the range represented. If you do, then use on of the shuffle answers provided by others. – Gazler Apr 10 '11 at 15:22
thnx for your code but the generated number depends on the size :( Deprecated: Call-time pass-by-reference has been deprecated, it uses lots of memory ! – Sourav Apr 10 '11 at 15:26
var_dump(getRandomNumbers(1, 15, 5)); function getRandomNumbers($min, $max, $count) i think something is wrong, i tried with these parameters (100,999,10); – Sourav Apr 10 '11 at 15:33
try this var_dump(getRandomNumbers(1, 5, 4)); – Sourav Apr 10 '11 at 15:42
yup, it worked perfectly :) but can't select as your answer as your function took 9.9999999999989E-5 seconds vs 5.9999999999949E-5 seconds, GOD Bless – Sourav Apr 10 '11 at 15:56
I think id you take it out of the function, replace var_dump with print_r and remove the error checking then it will. :P – Gazler Apr 10 '11 at 15:58

score 3 · Answer 6 · answered Apr 10 '11 at 15:18

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<=101;$i++) {
    $arr[] = $i;
}

shuffle($arr);

print_r($arr);

Output will look something like this:

Array
(
    [0] => 16
    [1] => 93
    [2] => 46
    [3] => 55
    [4] => 18
    [5] => 63
    [6] => 19
    [7] => 91
    [8] => 99
    [9] => 14
    [10] => 45
    [11] => 68
    [12] => 61
    [13] => 86
    [14] => 64
    [15] => 17
    [16] => 27
    [17] => 35
    [18] => 87
    [19] => 10
    [20] => 95
    [21] => 43
    [22] => 51
    [23] => 92
    [24] => 22
    [25] => 58
    [26] => 71
    [27] => 13
    [28] => 66
    [29] => 53
    [30] => 49
    [31] => 78
    [32] => 69
    [33] => 1
    [34] => 42
    [35] => 47
    [36] => 26
    [37] => 76
    [38] => 70
    [39] => 100
    [40] => 57
    [41] => 2
    [42] => 23
    [43] => 15
    [44] => 96
    [45] => 48
    [46] => 29
    [47] => 81
    [48] => 4
    [49] => 33
    [50] => 79
    [51] => 84
    [52] => 80
    [53] => 101
    [54] => 88
    [55] => 90
    [56] => 56
    [57] => 62
    [58] => 65
    [59] => 38
    [60] => 67
    [61] => 74
    [62] => 37
    [63] => 60
    [64] => 21
    [65] => 89
    [66] => 3
    [67] => 32
    [68] => 25
    [69] => 52
    [70] => 50
    [71] => 20
    [72] => 12
    [73] => 7
    [74] => 54
    [75] => 36
    [76] => 28
    [77] => 97
    [78] => 94
    [79] => 41
    [80] => 72
    [81] => 40
    [82] => 83
    [83] => 30
    [84] => 34
    [85] => 39
    [86] => 6
    [87] => 98
    [88] => 8
    [89] => 24
    [90] => 5
    [91] => 11
    [92] => 73
    [93] => 44
    [94] => 85
    [95] => 82
    [96] => 75
    [97] => 31
    [98] => 77
    [99] => 9
    [100] => 59
)

thnx for your code but the generated number depends on the size :( if i try to generate 3 number they are like 1, 3, 2 i want something like 1, 5, 15 [1-15 limit] i really appreciate your help :| — Sourav, Apr 10 '11 at 15:23
Ah, you question wasn't particularly clear – might be worth rewriting it to make it more clear! — Rich Bradshaw, Apr 10 '11 at 15:25

score 2 · Answer 7 · answered Apr 10 '11 at 15:18

2

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.

answered Apr 10 '11 at 15:18

Pete Wilson

8,610
6
39
51

score 2 · Answer 8 · answered Jun 20 '19 at 07:16

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 < 30000) {
for ($i = 0; $i < 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.

score 1 · Answer 9 · answered Apr 09 '13 at 20:30

1

This probably will solve your problem:

<?php print_r(array_rand(range(1,50), 5)); ?>

answered Apr 09 '13 at 20:30

Kamil Kwiecien

51
1
10

score 1 · Answer 10 · answered May 08 '14 at 08:26

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.'<br>';
        echo $output;
    }

}

randomNums(1100, 1000 ,890000, 899999);

score 0 · Answer 11 · edited Jul 26 '15 at 21:42

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";

stonyau · Answer 12 · 2016-01-05T10:18:07.527

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) < $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

score 0 · Answer 13 · edited Jul 22 '16 at 06:19

0

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 < $length; $i++)
{
    $random .= substr($data, (rand()%(strlen($data))), 1);
}
return $random;}

edited Jul 22 '16 at 06:19

Musakkhir Sayyed

7,012
13
42
65

answered Jul 22 '16 at 05:56

nileshkardate

21
1
1
7

score 0 · Answer 14 · answered Jun 15 '17 at 05:17

0

The best way to generate the unique random number is

<?php
     echo md5(uniqid(mt_rand(), true).microtime(true));
?>

answered Jun 15 '17 at 05:17

Kesavan Krishnan

27
3

Generating UNIQUE Random Numbers within a range

14 Answers14

Linked

Related