Transform flat array into a hierarchical, multi-dimensional array

Question

I have a standard array with key-value pairs - and I want to use the keys to transform it into a multi-dimensional array. The difficulty seems to be that I need to loop recursively the unknown number of new keys and turn them into a multi-dimensional array. In short, I want this:

$val[alfa.xray.uno] = "Some value";    
=> $val['alfa']['xray']['uno'] = "Some value";    

Example: (The code fails and also needs to handle N dimensions - but you get the idea..)

$arr['alfa.xray.uno'] = "Alfa X-Ray Uno";
$arr['alfa.yaho.duo'] = "Alfa Yaho Duo";
$arr['beta.xray.uno'] = "Beta X-Ray Uno";
$arr['beta.xray.duo'] = "Beta X-Ray Duo";
$arr['just-me'] = "Root-level item";

print_r( array_flat_to_multidimensional($arr) );

function array_flat_to_multidimensional($arr) {
    foreach($arr as $key=>$val) {
        $key = explode(".",$key);
        for($i=0; $i<count($key); $i++) {
            if($i==0) { $out[$key[$i]] = $val; }
            else if($i==1) { $out[$key[$i-1]][$key[$i]] = $val; }
            else if($i==2) { $out[$key[$i-2]][$key[$i-1]][$key[$i]] = $val; }
            else if($i==3) { $out[$key[$i-3]][$key[$i-2]][$key[$i-1]][$key[$i]] = $val; }
        }
    }
    return $out;
}

Perhaps RecursiveArrayIterator will do the trick?

Answer 1

You could use references to successively iterate through and build up the nested array structure:

$out = array();
foreach ($arr as $key=>$val) {
    $r = & $out;
    foreach (explode(".", $key) as $key) {
        if (!isset($r[$key])) {
            $r[$key] = array();
        }
        $r = & $r[$key];
    }
    $r = $val;
}
return $out;

Answer 2

use the recursion Luke

function ins(&$ary, $keys, $val) {
    $keys ? 
        ins($ary[array_shift($keys)], $keys, $val) :
        $ary = $val;
}

// test

$arr['alfa.xray.uno'] = "Alfa X-Ray Uno";
$arr['alfa.yaho.duo'] = "Alfa Yaho Duo";
$arr['beta.xray.uno'] = "Beta X-Ray Uno";
$arr['beta.xray.duo'] = "Beta X-Ray Duo";
$arr['just-me'] = "Root-level item";

$a = array();
foreach($arr as $k => $v)
    ins($a, explode('.', $k), $v);

print_r($a);

Answer 3

You can use a reference while walking though the array hierarchy levels:

function array_flat_to_multidimensional($arr) {
    $out = array();
    foreach ($arr as $compoundKey => $val) {
        $ref = &$out;
        foreach (explode(".", $compoundKey) as $key) {
            if (!array_key_exists($key, $ref)) $ref[$key] = array();
            $ref = &$ref[$key];
        }
        $ref = $val;
    }
    unset($ref);
    return $out;
}