how to make a nested list using a delimitted string or an array?

Question

my sql query gets me results like this :

Maths
Maths|Algebre
Maths|Algebre|Algebre 1
Maths|Algebre|Algebre 2
Maths|Algebre|Algebre 3
Maths|Analyse
Maths|Analyse|Analyse 1
Maths|Analyse|Analyse 2
Maths|Probabilité
physics

I have tryied many unsuccessful methods to use these strings to ultimately create an nested list in html.

I want to save them as a nested array like this :

$stack= array(
    "maths" =>  array(
            "Algebre" => array( "Algebre 1" ,"Algebre 2"),
            "Analyse" => array("Analyse 1","Analyse 2"),
            "Proba"
    ),
    "Physics"
) ;

and then I'd do something like this :

function print_list($array){
   echo "<ul>" ;
   foreach($array as $key => $item) {
       if (is_string($key)) echo "<li> $key" ;
       if (is_array($item)) print_list($item) ;
       else echo "<li> $item" ;
       echo "</li>" ;
    }
    echo "</ul>" ;
 }

 print_list($stack);

the problem is I can't produce the nested array. and the function is just a code I wrote on the fly here as an eventual solution once I get my nested array — Neo Mosaid
– Neo Mosaid, Commented Mar 8, 2020 at 11:19
I understand the problem, but you can at least use proper syntax in your expected array. As it is now it's not php and therefore this question should be locked in my opinion because the question is unclear — Andreas
– Andreas, Commented Mar 8, 2020 at 11:37

Jeto · Accepted Answer · 2020-03-08 14:42:07Z

Here's a possible implementation:

cleanupLines removes all "useless" lines from the original string (it will only keep the ones with leafs),
lineToArray takes line parts (after splitting by |) and calls itself recursively to generate an array for the given line,
array_merge_recursive merges all arrays into one.

Code:

function cleanupLines(array $lines): array
{
  foreach ($lines as $index => $line) {
    if ($index > 0 && strpos($line, $lines[$index - 1]) === 0) {
      unset($lines[$index - 1]);
    }
  }
  return $lines;
}

function lineToArray(array $lineParts): array
{
  if (count($lineParts) > 1) {
    return [$lineParts[0] => lineToArray(array_slice($lineParts, 1))];
  }
  return $lineParts;
}

$lines = preg_split('/\r?\n/', $input);
$lines = cleanupLines($lines);

$result = array_reduce($lines, static function (array $result, string $line): array {
  $lineParts = explode('|', $line);
  $arrayPart = lineToArray($lineParts);
  return array_merge_recursive($result, $arrayPart);
}, []);

print_r($result);

Demo: https://3v4l.org/0F1IM

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