I have an 2D array

```
$artists = [
    ["name" => "Post Malone", "song" => "Circles", "genre" => "Pop"],
    ["name" => "Camila Cabello", "song" => "Liar", "genre" => "Pop"],
    ["name" => "Tones and I", "song" => "Dance Monkey", "genre" => "Alternative"],
    ["name" => "Billie Eilish", "song" => "Bad Guy", "genre" => "Alternative"],
];

```

I'm trying to write a function that organized the array by genre and group different artist by genre. My output should looks like this:

```
array (
  'Pop' =>
  array (
    0 => 'Post Malone',
     1 => 'Camila Cabello',
   ),
  'Alternative' =>
   array (
     0 => 'Tones and I',
     1 => 'Billie Eilish',
   ),
)

```

I have tried to construct the outter array first 

```
function organizer($artists) {
    $genre = array();
    for ($i = 0; $i < count($artists); $i++) {
        $outterArr = array_push ($artists[$i]["genre"],$genre);
        return $outterArr;
    }

}

```

But stuck on how to construct an new array inside the outer array.
I'm very new to programming and php. please bare my skill, thanks!