How to implement a function with array

<?php
class FileOwners
{
    public static function groupByOwners($files)
    {
        return NULL;
    }
}

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

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

Implement a groupByOwners function :

• Accepts an associative array containing the file owner name for each file name.

• Returns an associative array containing an array of file names for each owner name, in any order.

  For example

Given the input:

["Input.txt" => "Randy", "Code.py" => "Stan", "Output.txt" => "Randy"]

groupByOwners returns:

["Randy" => ["Input.txt", "Output.txt"], "Stan" => ["Code.py"]]

Answer

<?php
class FileOwners
{
    public static function groupByOwners($files)
    {
        $result=array();
        foreach($files as $key=>$value)
        {
            $result[$value][]=$key;
        }
        return $result;
    }
}

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

Output:

Array
(
    [Randy] => Array
        (
            [0] => Input.txt
            [1] => Output.txt
        )

    [Stan] => Array
        (
            [0] => Code.py
        )

)