How do I create a multi-dimensional array with a recursive function in PHP?

Question

I have an employees table and some of the employees are managers. I need a function that takes an employee ID and creates a multi-dim array with all the employees that report to them. So far I was able to print the tree:

function drillDownStaff($emplid){
    $conn = db_connect();

    $sql = "SELECT
            employees.EmployeeID, employees.ManagerID
        FROM
            employees
        WHERE
            employees.ManagerID = '".$emplid."';
    $result = mysql_query($sql,$conn);
    while($row = mysql_fetch_assoc($result)){
        echo "<ul>";
        echo "<li>".$row['FullName'];
        drillDownStaff($row['EmployeeID']);
        echo "</li>";
        echo "</ul>";
    }
}

This will print out a nice manager->employee tree:

John
- Jane
  - Paul
  - Maria
  - Mark
- Tony
- Blane
Colleen
- Roxy
- Foxy
Lilly
Maureen

But what I'd like is the recursive function to return a multi-dim array with the employee tree like so:

array(
    [5] => array(
        [FullName] => John
        [...] => Other emp details
        [manages] => array(
            [6]=>array(
                [FullName]=>Jane
                [...]=>other emp details
                [manages]=> array(Pauls' details)
            )
            [7]=>array(...) // emp details again
        )
    )

)

Is this possible?

Yes, it is possible, but will take some work. What have you tried? — alanmm
– alanmm, Commented Sep 29, 2015 at 16:30
I tried too many things to remember. The best I was able to get was a big flat array with all emps in order but not a proper multi-dim array. I think I'm having a hard time understanding the scope of the arrays and sub-arrays when passing through the recursive function. — Sergiu Z
– Sergiu Z, Commented Sep 29, 2015 at 16:33
You know just reading this immediately I think, the easiest of ways to accomplish this is not necessarily recursion. All the pulls to your database is dangerous for intrusion. You could try two pulls to your DB. 1. Pull all managers. 2. Pull all employees. Then create an empty multi-dim arrays and foreach manager push to [i][] and for each employee if they report to the manager push [i][j]. Does that make sense? — Chris
– Chris, Commented Sep 29, 2015 at 16:34
To build such array, it would be better if we knew how the query result array is inside. Can you var_dump it and show its structure? — alanmm
– alanmm, Commented Sep 29, 2015 at 16:39
Why are you using the $i variable in your loop with the conditional statements? Both of them will always equal true. — Cameron Spanos
– Cameron Spanos, Commented Sep 29, 2015 at 16:54

Phylogenesis · Accepted Answer · 2015-09-30 08:51:22Z

A recursive function to build the staff tree is as follows. Bear in mind this isn't very efficient, so don't expect it to be particularly performant if you have a tree of hundreds/thousands of staff members.

function buildStaffTree($managerId = null) {
    global $staff;

    $subordinates = array_values(array_filter(
        $staff,
        function ($staffMember) use ($managerId) {
            return $staffMember['manager'] === $managerId;
        }
    ));

    if ($managerId === null) {
        // Tree root - only enumerate the top-level managers
        return array_map(
            function ($subordinate) {
                return buildStaffTree($subordinate['id']);
            },
            $subordinates
        );
    } else {
        $manager = array_values(array_filter(
            $staff,
            function ($staffMember) use ($managerId) {
                return $staffMember['id'] === $managerId;
            }
        ))[0];

        return [
            'id'      => $manager['id'],
            'name'    => $manager['name'],
            'manages' => array_map(
                function ($subordinate) {
                    return buildStaffTree($subordinate['id']);
                },
                $subordinates
            )
        ];
    }
}

An example of this code running is available here.

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