PHP: Get all combinations of multiple arrays (preserves keys)

get_combinations.php

<?php

function get_combinations($arrays) {
	$result = array(array());
	foreach ($arrays as $property => $property_values) {
		$tmp = array();
		foreach ($result as $result_item) {
			foreach ($property_values as $property_value) {
				$tmp[] = array_merge($result_item, array($property => $property_value));
			}
		}
		$result = $tmp;
	}
	return $result;
}

$combinations = get_combinations(
	array(
		'item1' => array('A', 'B'),
		'item2' => array('C', 'D'),
		'item3' => array('E', 'F'),
	)
);

var_dump($combinations);

?>

output.txt

array (size=8)
  0 => 
    array (size=3)
      'item1' => string 'A' (length=1)
      'item2' => string 'C' (length=1)
      'item3' => string 'E' (length=1)
  1 => 
    array (size=3)
      'item1' => string 'A' (length=1)
      'item2' => string 'C' (length=1)
      'item3' => string 'F' (length=1)
  2 => 
    array (size=3)
      'item1' => string 'A' (length=1)
      'item2' => string 'D' (length=1)
      'item3' => string 'E' (length=1)
  3 => 
    array (size=3)
      'item1' => string 'A' (length=1)
      'item2' => string 'D' (length=1)
      'item3' => string 'F' (length=1)
  4 => 
    array (size=3)
      'item1' => string 'B' (length=1)
      'item2' => string 'C' (length=1)
      'item3' => string 'E' (length=1)
  5 => 
    array (size=3)
      'item1' => string 'B' (length=1)
      'item2' => string 'C' (length=1)
      'item3' => string 'F' (length=1)
  6 => 
    array (size=3)
      'item1' => string 'B' (length=1)
      'item2' => string 'D' (length=1)
      'item3' => string 'E' (length=1)
  7 => 
    array (size=3)
      'item1' => string 'B' (length=1)
      'item2' => string 'D' (length=1)
      'item3' => string 'F' (length=1)

Here's a PHP version of dernoun's Java solution.

function getNumberOfOptions(array $arr): void {
    $n = count($arr);
    $indices = array_fill(0, $n, 0);
    while(true) {

        // grab current combination for the indices.
        for($i = 0; $i < $n; $i++) {
            echo $arr[$i][$indices[$i]] . ' ';
        }
        echo "\n";

        // Find the rightmost array that has more
        // elements left after the current element
        // in that array
        $next = $n - 1;
        while($next >= 0 &&
            ($indices[$next] + 1 >=
            count($arr[$next]))
        ) {
            $next--;
        }

        // No such array is found so no more
        // combinations left
        if ($next < 0)
            break;

        // If found move to next element in that
        // array
        $indices[$next]++;

        // For all arrays to the right of this
        // array current index again points to
        // first element
        for($i = $next + 1; $i < $n; $i++) {
            $indices[$i] = 0;
        }
    }
}

Or if we change the function to instead return the array of combinations rather than print them, it would look like this:

function get_combinations(array $arrays): array {
    $n = count($arrays);
    $indices = array_fill(0, $n, 0);
    $combinations = [];
    while(true) {

        // grab current combination for the indices.
        $combination = [];
        for($i = 0; $i < $n; $i++) {
            $combination[] = $arrays[$i][$indices[$i]];
        }
        $combinations[] = $combination;

        // Find the rightmost array that has more
        // elements left after the current element
        // in that array
        $next = $n - 1;
        while($next >= 0 && 
                ($indices[$next] + 1 >=
                count($arrays[$next]))
        ) {
            $next--;
        }

        // No such array is found so no more
        // combinations left
        if ($next < 0)
            break;

        // If found move to next element in that
        // array
        $indices[$next]++;

        // For all arrays to the right of this
        // array current index again points to
        // first element
        for($i = $next + 1; $i < $n; $i++) {
            $indices[$i] = 0;
        }
    }
    return $combinations;
}

Thanks! :)