Generate array of random unique numbers in PHP

Question

I\'m trying to generate an array of random numbers from 0-n then shuffle (but ensure that the keys and values DO NOT match).

For example:

0 => 3
1         


        

Answer 1

$max = 5;
$done = false;
while(!$done){
    $numbers = range(0, $max);
    shuffle($numbers);
    $done = true;
    foreach($numbers as $key => $val){
        if($key == $val){
            $done = false;
            break;
        }
    }
}

Answer 2

Naive solution:

$n = 10;
$rands = array();
for($i=0; $i<$n;$i++) {
  $ok = false;
  while(!$ok) {
    $x=mt_rand(0,$n-1);
    $ok = !in_array($x, $rands) && $x != $i;
  }
  $rands[$i]=$x;
}

var_dump($rands);

Efficient solution:

$n = 100;  
$numbers = range(0, $n-1);
$rands = array();
for ($i=0; $i < $n; $i++) {
  $ok = false;
  while (!$ok) {
    $x = array_rand($numbers);
    $ok = !in_array($numbers[$x], $rands) && $numbers[$x] != $i;
  }
  $rands[$i] = $numbers[$x];
  unset($numbers[$x]);
}

var_dump($rands);

edit: s/rand/mt_rand/

edit #2: both solutions can end up in a deadlock, as mentioned by @AMayer. I stand corrected.

Answer 3

Here's a rather long, but also pretty efficient solution, I believe. Contrary to other solutions posted here, this cannot deadlock (unless $size<2), and this will not do a full shuffle every time one value doesn't fit. Instead, it will only replace that value with another, random value.

function unique_list($size=5) {

    function all_unique($numbers) {
        foreach ($numbers as $key=>$value)
            if ($key==$value) return false;
        return true;
    }
    function flip($a, $b, &$numbers) {
        $numbers[$a] = $numbers[$a] + $numbers[$b];
        $numbers[$b] = $numbers[$a] - $numbers[$b];
        $numbers[$a] = $numbers[$a] - $numbers[$b];
    }

    $flip_count = 0;
    $numbers = range(0,$size-1);
    shuffle($numbers);

    while (!all_unique($numbers)) {
        foreach ($numbers as $key=>$value) {
            if ($key==$value) {
                flip($key, rand(0,$size-1), $numbers);
                $flip_count++;
                break;
            }
        }
    }

    printf("Flipped %d values\n", $flip_count);
    return $numbers;

}

$list = unique_list(10);
print_r($list);

The above will print something similar to

Flipped 1 value(s)
Array
(
    [0] => 2
    [1] => 5
    [2] => 7
    [3] => 9
    [4] => 6
    [5] => 3
    [6] => 1
    [7] => 8
    [8] => 0
    [9] => 4
)

Answer 4

The approach here is to create a range of numbers from 0 to n, and then shuffle. We then look for key value matches, and swap pairs of them. If we don't have a pair to swap, we swap with the last item, unless the item is the last item, then we swap with the first.

<?php
$n = 5;
$values = range(0, $n);
shuffle($values);
$matched = array_filter($values, function($v, $k) {return $k === $v;}, ARRAY_FILTER_USE_BOTH);
foreach(array_chunk($matched, 2) as list($a, $b)) {
    if($b === null) {
        $swap_key = array_key_last($values);
        if($swap_key == $a) {
            $swap_key = array_key_first($values);
        }
        list($values[$a], $values[$swap_key]) = [$values[$swap_key], $a];
    } else {
        list($values[$a], $values[$b]) = [$b, $a];
    }
}

Example shuffle when n is 5:

array (
  0 => 0,
  1 => 5,
  2 => 1,
  3 => 3,
  4 => 4,
  5 => 2,
)

Here we have matches for keys:

0, 3 and 4.

So we swap the values for keys 0 and 3, and 4 with the last.

array (
  0 => 3,
  1 => 5,
  2 => 1,
  3 => 0,
  4 => 2,
  5 => 4,
)

(array_key_first could be swapped for 0 given the range here. I've left it as it is more explicit.)

Answer 5

A even shorter solution:

$random_number_array = range(0, 100);
shuffle($random_number_array );
$random_number_array = array_slice($random_number_array ,0,10);

print_r($random_number_array);

Result will be:

[0] => 53
[1] => 6
[2] => 16
[3] => 59
[4] => 8
[5] => 18
[6] => 62
[7] => 39
[8] => 22
[9] => 26

Answer 6

This will generate an array with 10 random numbers from 0 to 100:

array_map(function () {
       return rand(0, 100);
   }, array_fill(0, 10, null)
);

Result:

array(10) {
  [0]=>
  int(15)
  [1]=>
  int(97)
  [2]=>
  int(20)
  [3]=>
  int(64)
  [4]=>
  int(57)
  [5]=>
  int(38)
  [6]=>
  int(16)
  [7]=>
  int(53)
  [8]=>
  int(56)
  [9]=>
  int(22)
}

Explanation:

• array_fill(0, 10, null) will generate an array with 10 empty items
• array_map Applies the callback (first argument) to each item of the array it receives (second argument). In this example, we just return a random number for each array item.

Playground: https://3v4l.org/FffN6