Array elements permutations with preserving keys in PHP

Question

I have an array:

[0 => 'перший', 1 => 'другий', 2 => 'третій']

I need to get:

[0 => 'перший', 1 => 'другий', 2 => 'третій'],
[0 => 'перший', 2 = > 'третій', 1 => 'другий'],
[1 => 'другий, 0 => 'перший', 2 => 'третій'],
[1 => 'другий ', 2 = > 'третій, 0 => 'перший'],
[2 => 'третій', 0 => 'перший', 1 = > 'другий'],
[2 => 'третій', 1 => 'другий', 0 = > 'перший']

I wrote a function:

function permutations($inArray, &$returnArray = [], $inProcessedArray = [])
{
    if (count($inArray) === 1)
    {
        $returnArray[] = array_merge($inProcessedArray, $inArray);
    }
    else
    {
        foreach($inArray as $key => $value)
        {
            $copyArray = $inArray;
            unset($copyArray[$key]);
            permutations($copyArray, $returnArray, array_merge($inProcessedArray, [$key => $value]));
        }
    }
}

But this returns array elements permutations without preserving keys
Any suggestions? Thanks in advance

So you are basically permuting the order and keeping the key/value association, right? If so, I think I'd make two total passes. The first would only permute the keys to get your different orders. The second would then build the output array taking the source array with the permuted key order. — Chris Haas
– Chris Haas, Commented Jul 22, 2022 at 14:29

Progrock · Accepted Answer · 2022-07-22 16:18:28Z

1

Using the generator permutations from: https://stackoverflow.com/a/27160465/

$hash = [
    0=>'Apple',
    1=>'Banana',
    2=>'Peach'
];

function permutations(array $elements)
{
    if (count($elements) <= 1) {
        yield $elements;
    } else {
        foreach (permutations(array_slice($elements, 1)) as $permutation) {
            foreach (range(0, count($elements) - 1) as $i) {
                yield array_merge(
                    array_slice($permutation, 0, $i),
                    [$elements[0]],
                    array_slice($permutation, $i)
                );
            }
        }
    }
}

$result = [];
foreach(permutations(array_keys($hash)) as $keys) {
    $row = [];
    foreach($keys as $k) {
        $row[$k] = $hash[$k];
    }
    $result[] = $row;
}
var_export($result);

Output:

array (
  0 => 
  array (
    0 => 'Apple',
    1 => 'Banana',
    2 => 'Peach',
  ),
  1 => 
  array (
    1 => 'Banana',
    0 => 'Apple',
    2 => 'Peach',
  ),
  2 => 
  array (
    1 => 'Banana',
    2 => 'Peach',
    0 => 'Apple',
  ),
  3 => 
  array (
    0 => 'Apple',
    2 => 'Peach',
    1 => 'Banana',
  ),
  4 => 
  array (
    2 => 'Peach',
    0 => 'Apple',
    1 => 'Banana',
  ),
  5 => 
  array (
    2 => 'Peach',
    1 => 'Banana',
    0 => 'Apple',
  ),
)

answered Jul 22, 2022 at 16:18

Progrock

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1 Comment

Progrock Over a year ago

If anyone can find a more elegant permutation function, please link or edit accordingly.

Progrock · Accepted Answer · 2022-07-22 15:05:40Z

This is over-egging the pudding somewhat. But given such a small array, we can loop over many combinations and filter accordingly.

I'm sure there is something more elegant, but this does the trick.

<?php
$result = [];
for($i=0; $i<3; $i++) {
    for($j=0; $j<3; $j++) {
        for($k=0; $k<3; $k++) {
            $row = [$i=>$hash[$i], $j=>$hash[$j], $k=>$hash[$k]];                       
            if(count($row) == 3)
                $result[] = $row;
        }
    }
}

Output:

array (
  0 => 
  array (
    0 => 'Apple',
    1 => 'Banana',
    2 => 'Peach',
  ),
  1 => 
  array (
    0 => 'Apple',
    2 => 'Peach',
    1 => 'Banana',
  ),
  2 => 
  array (
    1 => 'Banana',
    0 => 'Apple',
    2 => 'Peach',
  ),
  3 => 
  array (
    1 => 'Banana',
    2 => 'Peach',
    0 => 'Apple',
  ),
  4 => 
  array (
    2 => 'Peach',
    0 => 'Apple',
    1 => 'Banana',
  ),
  5 => 
  array (
    2 => 'Peach',
    1 => 'Banana',
    0 => 'Apple',
  ),
)

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