Build a unique string list from multidimensional array items

Question

I have a multidimensional array:

$items = array(
   array("A1", "A2", "A3"),
   array("B1","B2","B3","B4"),
   array("C1","C2","C3","C4","C5"),
   array("D1","D2","D3")); 

I need to build a list of unique strings, and each should contain one item from each array, like this:

A1 B1 C1 D1 ,
A1 B1 C1 D2 ,
A1 B1 C1 D3 ,
A1 B1 C2 D1 ,
A1 B1 C2 D2 ,
etc...

Example data above should produce 180 combinations (3*4*5*3=180).

The difficulty is that the code (in best case) should work for any number of arrays. Not just for 4 as in the example above.

For example, I would add: array("E1", "E2"); and code should still work.

A simpler version might be working with fixed set of arrays, for example 4 (as in the example above).

Of course I can use for loops, but in this case it will be required to add another for loop, each time I add another array of data (not so universal, right?).

Here's what I tried, but it didn't work out:

$items = array(
   array("A1", "A2", "A3"),
   array("B1","B2","B3","B4"),
   array("C1","C2","C3","C4","C5"),
   array("D1","D2","D3"));

$depth = count($items);
$index = $depth - 1;

for ($i = 0; $i <= $index; $i++) {
   $depth2 = count($items[$i]);
   $index2 = $depth2 - 1;
   echo "SET: ";
   for ($i2 = 0; $i2 <= $index2; $i2++) {
      echo $items[$i2][$i].", ";
   }
   echo "<br>";
}

Expected result is the list of 180 unique strings, like:

A1 B1 C1 D1 ,
A1 B1 C1 D2 ,
A1 B1 C1 D3 ,
A1 B1 C2 D1 ,
A1 B1 C2 D2 ,
etc...

Answer 1

You can use recursion to build the result set similar to the way you might permute an array with backtracking. The idea is to include each item one at a time from each array and add it to the in-progress result, then recurse on that possibility. After exploring all of the result possibilities for a given element, we discard it from further consideration and move on to the next element, repeating the process.

<?php

function combos($items, &$curr=[], &$res=[], $i=0) {
    if ($i >= count($items)) {
        $res[]= $curr;
    }
    else {
        foreach ($items[$i] as $e) {
            $curr[]= $e;
            combos($items, $curr, $res, $i + 1);
            array_pop($curr);
        }
    }

    return $res;
}

$items = [
    ["A1", "A2", "A3"],
    ["B1","B2","B3","B4"],
    ["C1","C2","C3","C4","C5"],
    ["D1","D2","D3"]
];
$i = 0;

foreach (combos($items) as $combo) {
    echo str_pad($i++ . ": ", 5, " ", false) . implode(" ", $combo) . "\n";
}

Output:

  0: A1 B1 C1 D1
  1: A1 B1 C1 D2
  2: A1 B1 C1 D3
  3: A1 B1 C2 D1
  4: A1 B1 C2 D2
  5: A1 B1 C2 D3
  6: A1 B1 C3 D1
  7: A1 B1 C3 D2
...
172: A3 B4 C3 D2
173: A3 B4 C3 D3
174: A3 B4 C4 D1
175: A3 B4 C4 D2
176: A3 B4 C4 D3
177: A3 B4 C5 D1
178: A3 B4 C5 D2
179: A3 B4 C5 D3