Permutations of an array of arrays of strings

Just for those wanting a PHP translation:

function factor_permutations($lists) {

    $permutations = array();
    $iter = 0;

    while (true) {

        $num = $iter++;
        $pick = array();

        foreach ($lists as $l) {
            $r = $num % count($l);
            $num = ($num - $r) / count($l);
            $pick[] = $l[$r];
        }

        if ($num > 0) break;
        $permutations[] = $pick;
    }

    return $permutations;
}

print_r(factor_permutations(array(array('a', 'b'), array('1', '2', '3'), array('foo', 'bar'))));

for ($i = 0; i < sizeof($Type); $i++) {
  for ($j = 0; j < sizeof($Size); $j++) {
     for ($k = 0; k < sizeof($Colour); $k++) {
       echo $Type[i] . $Size[j] . $Colour[k];
     }
  }
}

Well I am not clever enough to comprehend ikegami's solution but I was able to convert it to Javascript for my purposes. I don't know how it works but it is brilliant!

lists = [["a","b"],["x","y"],["1","2","3"]] 

function factorPermutations(lists) {  

permutations = []
$iter = 0;

while (1) {

    $num = $iter++;
    $pick = []; 

    for (l in lists) {
        $r = $num % (lists[l].length );
        $num = ($num - $r) / lists[l].length;
        $pick.push( lists[l][$r])
    } 
    if ($num > 0) break;

    permutations.push( $pick);
}
    return permutations
} 

console.log(factorPermutations(lists))

Yeah, I left some of the $ signs on variables from the PHP version.

Supposing you have only one nesting level, what you want is:

$my_ar[group1][0].(rest_of_the_group_perms[0])
$my_ar[group1][0].(rest_of_the_group_perms[1])
...
$my_ar[group1][N].(rest_of_the_group_perms[K])

that is, you can see the problem as having to join two lists/arrays. The first being the first subarray of your array and the second being the (recursively already made) rest.

So you need a function like this:

perms($my_arr) {
   foreach($elem in $group1) {
      $return_list[] = $elem.$rest;
   }
}

where $group1 is the first subarray of your array and $group_rest is what is left. So:

perms($my_arr) {
   $group1 = head($my_arr);
   $group_rest = tail($my_arr);

   $rest = perms($group_rest);
   $return_list = array();
   foreach($elem in $group1) {
      $return_list[] = "$elem, $rest";
   }
   return $return_list;
}

but $rest is also an array so you have to loop over that too:

perms($my_arr) {
   $group1 = head($my_arr);
   $group_rest = tail($my_arr);

   $rest = perms($group_rest);
   $return_list = array();
   foreach($elem in $group1) {
      foreach($relem in $rest) {
          $return_list[] = $elem.$relem;
      }
   }
   return $return_list;
}

add the ending condition (null $group_rest) and you are set:

perms($my_arr) {
   $group1 = head($my_arr);
   $group_rest = tail($my_arr);

  if (length($group_rest) == 0) 
       $rest = array();
  else
       $rest = perms($group_rest);
   $return_list = array();
   foreach($elem in $group1) {
      foreach($relem in $rest) {
          $return_list[] = $elem.$relem;
      }
   }
   return $return_list;
}