file_owner.php

<?php

//solution for Test Dome PHP File Owner Task

class FileOwners
{
    public static function groupByOwners($files)
    {
        $owners = array_unique($files);

        $sorted = array();

        foreach ($owners as $owner) {
            $sorted[$owner] = array();
        }

        foreach ($files as $file => $owner) {
            array_push($sorted[$owner], $file);
        }

        return $sorted;
    }
}

$files = array
(
    "Input.txt" => "Randy",
    "Code.py" => "Stan",
    "Output.txt" => "Randy",
);

print_r(FileOwners::groupByOwners($files));