Reverse flatted array to multidimensional

Question

In another thread i asked about flatten an array with a specific style to get something like this:

array(4) {
  ["one"]=> string(9) "one_value"
  ["two-four"]=> string(10) "four_value"
  ["two-five"]=> string(10) "five_value"
  ["three-six-seven"]=> string(11) "seven_value"
}

I've got some very good help there, but now im wondering how would i reverse this method to get again the same original array:

array(
    'one' => 'one_value',
    'two' => array
        (
            'four' => 'four_value',
            'five' => 'five_value'
        ),

    'three' => array
        (
            'six' => array
                (
                    'seven' => 'seven_value'
                )

        )
)

I've tried with recursive method but with no luck. I thank all the help in advance!

score 4 · Accepted Answer · answered Feb 23 '12 at 19:43

function expand($flat) {
    $result = array();
    foreach($flat as $key => $val) {
        $keyParts = explode("-", $key);
        $currentArray = &$result;
        for($i=0; $i<count($keyParts)-1; $i++) {
            if(!isSet($currentArray[$keyParts[$i]])) {
                $currentArray[$keyParts[$i]] = array();
            }
            $currentArray = &$currentArray[$keyParts[$i]];
        }
        $currentArray[$keyParts[count($keyParts)-1]] = $val;
    }
    return $result;
}

Note that the code above is not tested and is given only to illustrate the idea. The & operator is used for $currentArray to store not the value but the reference to some node in your tree (implemented by multidimensional array), so that changing $currentArray will change $result as well.

Although i don't understand very well how (and how to) work with references, this function works pretty good and do as intended! :) — MGP, Feb 23 '12 at 19:53

score 0 · Answer 2 · answered Feb 23 '12 at 20:22

Here is an efficient recursive solution:

$foo = array(
  "one" => "one_value",
  "two-four" => "four_value",
  "two-five" => "five_value",
  "three-six-seven" => "seven_value"
);



function reverser($the_array) {
   $temp = array();
   foreach ($the_array as $key => $value) {
      if (false != strpos($key, '-')) {
         $first = strstr($key, '-', true);
         $rest = strstr($key, '-');
         if (isset($temp[$first])) {
            $temp[$first] = array_merge($temp[$first], reverser(array(substr($rest, 1) => $value)));
         } else {
            $temp[$first] = reverser(array(substr($rest, 1) => $value));
         }
      } else {
         $temp[$key] = $value;
      }
   }
   return $temp;
}

print_r(reverser($foo));

strstr(___, ___, true) only works with PHP 5.3 or greater, but if this is a problem, there's a simple one-line solution (ask if you'd like it).

Reverse flatted array to multidimensional

2 Answers2

Linked