- array_column: documentation ( source)
<?php
$episodes = array_column([
1 => [
['el' => 1, 's' => 1, 'ep' => 101],
['el' => 1, 's' => 1, 'ep' => 102],
['el' => 1, 's' => 2, 'ep' => 103],
['el' => 1, 's' => 3, 'ep' => 104],
]
]);
array_column($episodes[1], 'ep', 's');