How to Generate the Cartesian Product of Multiple Arrays in PHP?

Generating the Cartesian Product of Multiple Arrays in PHP

Introduction:
Producing combinations from multiple arrays is a common task in programming. The Cartesian product of these arrays is a list of all possible combinations of elements from the input arrays.

Problem:
Given an array with multiple subarrays, we want to generate a table containing all unique combinations of elements from those subarrays. For instance, if we have two subarrays:

$array[0][0] = 'apples';
$array[0][1] = 'pears';
$array[0][2] = 'oranges';

$array[1][0] = 'steve';
$array[1][1] = 'bob';

We expect the output to be:

Array 0            Array 1
apples             steve
apples             bob
pears              steve
pears              bob

Solution: Cartesian Product
This problem requires calculating the Cartesian product, which generates all possible combinations of elements from multiple arrays.

Implementation:
One approach to calculate the Cartesian product involves using a recursive function. Here's an example implementation:

function array_cartesian() {
    $_ = func_get_args();
    if(count($_) == 0)
        return array(array());
    $a = array_shift($_);
    $c = call_user_func_array(__FUNCTION__, $_);
    $r = array();
    foreach($a as $v)
        foreach($c as $p)
            $r[] = array_merge(array($v), $p);
    return $r;
}

This function takes multiple arrays as inputs. It iterates through the first array and combines each of its elements with all possible combinations of the remaining arrays. The result is a list of all unique combinations.

Example:
Let's apply the solution to our example:

$cross = array_cartesian(
    array('apples', 'pears',  'oranges'),
    array('steve', 'bob')
);

print_r($cross);

This will output:

Array
(
    [0] => Array
        (
            [0] => apples
            [1] => steve
        )

    [1] => Array
        (
            [0] => apples
            [1] => bob
        )

    [2] => Array
        (
            [0] => pears
            [1] => steve
        )

    [3] => Array
        (
            [0] => pears
            [1] => bob
        )
)

Which matches our expected output.

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