- print_r: documentation ( source)
<?php
$array = [
'visitPoints'=>[
20=>[2,5,6,8,10,11],
35=>[2,5,6],
57=>[1]
],
'islands'=>[
20=>[5,10,11],
35=>[5,6]
],
'animals'=>[
20=>[5,11],
35=>[]
]
];
$result = [
20=>[5,11],
35=>[],
57=>[]
];
print_r($result);