http://stackoverflow.com/questions/17959127/php-array-join-each-sub-array-together-probability NOTE: Does not check for empty input sets which are invalid.

example-17959127.php

<?php
/**
 * @link https://gist.github.com/hakre/c131eb6e5428b9b5a06a
 * @link http://stackoverflow.com/a/18170304/367456
 * @link https://eval.in/private/67411a840f2de9
 */
 
// input
$array = [
    ['a', 'b', 'c'],
    ['e', 'f', 'g'],
    ['h', 'i', 'j', 'k', 'l'],
];

/**
 * Cartesian Product Generator (array-based)
 */
function cartesianProduct(array $array)
{
   // exit early
    if (!$array)
    {
        return;
    }
     
    // obtain length of array
    $length = count($array);
     
    // obtain length of elements in the array
    $lengths = array_map('count', $array);
     
    // obtain array keys (not visible in question)
    $arrayKeys = array_keys($array);
     
    // obtain array sub-keys (not visible in question)
    $keys = array_map('array_keys', $array);
     
    // define the order (last sub-array first in question)
    $order = array_keys(
        array_reverse($arrayKeys, TRUE)
    );
     
    // define counter per each key
    $counters = array_combine(
        $arrayKeys,
        array_fill(0, $length, 0)
    );
     
    // working loop
    $valid = TRUE;
    while ($valid)
    {
        // create tuple
        $values = $ykeys = [];

        foreach ($array as $key => $sub)
        {
            $values[] =  $sub[$keys[$key][$ykeys[] = $counters[$key]]];
        }
         
        
        yield $ykeys => $values; 
     
        // count up
        foreach ($order as $key)
        {
            if (++$counters[$key] == $lengths[$key])
            {
                $counters[$key] = 0;
                continue;
            }
            continue 2;
        }
        $valid = FALSE;
    };
}

foreach (cartesianProduct($array) as $key => $value) {
    echo implode(',', $key), ' => ', implode(',', $value), "\n";
}