Any php built-in function to filter an associative array? for example

[
  'user1' => ['userid' => '001', 'city' => 'city1'],
  'user2' => ['userid' => '002', 'city' => 'city2'],
  'user3' => ['userid' => '003', 'city' => 'city3'],
]

to

[
  'user1' => ['userid' => '001'],
  'user2' => ['userid' => '002'],
  'user3' => ['userid' => '003'],
]

or

[
  '001',
  '002',
  '003',
]