Combinations, Dispositions and Permutations in PHP

Question

What is the most efficient way to generate all the combinations, dispositions and permutations of an array in PHP?

Answer 1

Here is code to get all permutations:

http://php.net/manual/en/function.shuffle.php#90615

With the code to get the power set, permutations are those of maximal length, the power set should be all combinations. I have no idea what dispositions are, so if you can explain them, that would help.

Answer 2

You can use this class: http://pear.php.net/package/Math_Combinatorics

and use it like:

$combinatorics = new Math_Combinatorics;

$words_arr = array(
    'one'   => 'a',
    'two'   => 'b',
    'three' => 'c',
    'four'  => 'd',
    );

for ($i=count($words_arr)-1;$i>=1;$i--) {
    echo '<br><br>' . $i . ':<br>';
    $combinations_arr = $combinatorics->combinations($words_arr, $i);
    foreach ($combinations_arr as $combinations_arr_item) {
        echo implode(', ', $combinations_arr_item) . '<br>';
    }
}

Answer 3

I'd like to suggest my solution of a CombinationsGenerator, which generates combinations of array items.

It's limited to all combinations are of the full length, and not repeats any item. But I believe implementation would not be too hard.

class CombinationsGenerator
{
    public function generate(array $list): \Generator
    {
        if (count($list) > 2) {
            for ($i = 0; $i < count($list); $i++) {
                $listCopy = $list;

                $entry = array_splice($listCopy, $i, 1);
                foreach ($this->generate($listCopy) as $combination) {
                    yield array_merge($entry, $combination);
                }
            }
        } elseif (count($list) > 0) {
            yield $list;

            if (count($list) > 1) {
                yield array_reverse($list);
            }
        }
    }
}

$generator = new \CombinationsGenerator();

foreach ($generator->generate(['A', 'B', 'C', 'D']) as $combination) {
    var_dump($combination);
}

It's in PHP7 style, it uses a \Generator 'cause I believe there are good reasons for doing it.