Generate array of random unique numbers in PHP - 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 => 2
2 => 4
3 => 0
4 => 1
Note that both keys and values are from 0-4 but none of the keys and values are the same.
Any thoughts?

Answer 1

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 2

$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 3

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
If you need to make sure each generated number is unique:
$uniqueNumbers = 100;
$picked = [];
$uniqueRandomNumbers = array_map(function () use(&$picked, $uniqueNumbers) {
do {
$rand = rand(0, $uniqueNumbers);
} while(in_array($rand, $picked));
$picked[] = $rand;
return $rand;
}, array_fill(0, $uniqueNumbers, null));
https://3v4l.org/mSWBo#v8.0.9

Answer 4

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 5

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 6

What's about combining range(...) (for generating the original array first), shuffle(...) (to randomize the array), and array_intersect_assoc(...) (for checking the result array)?
$numbers = range(0, 4);
do {
shuffle($numbers); // print_r($numbers);
$matchingKeyValuePairs = array_intersect_assoc(array_keys($numbers), array_values($numbers)); // print_r($matchingKeyValuePairs);
} while (! empty($matchingKeyValuePairs));
This solution might bring some performance issues for big numbers of elements. But it can be extended by a logic for dealing with the $matchingKeyValuePairs. So while now the logic is like "IF there are matchingKeyValuePairs THEN try it again", a much more efficient logic migth be "IF there are matchingKeyValuePairs THEN cut the matchingKeyValuePairs from the array, randomize this sub-array (multiple times, if needed), and merge it back".

Answer 7

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 8

public function getUniqueArray($value, $total)
{
$array = [];
for ($i = 0; $i < $value; $i++) {
$rand = rand(0, $total);
if (in_array($rand, $array))
$i--;
else
array_push($array, rand(0, $total));
}
return $array;
}