Online PHP editor | output for V6uFf

<?php $array = [ [ 'id' => 1, 'some_key' => 'some_value', 'attribute' => [ 'id' => 45, 'cat_id' => 1 ], 'sub' => [ 'id' => 17, 'some_key' => 'some_value', 'attribute' => [ 'id' => 47, 'cat_id' => 17 ], ], ], [ 'id' => 2, 'some_key' => 'some_value', 'sub' => [ 'id' => 19, 'some_key' => 'some_value', ], ] ]; $childArray = []; function collectIDs($arr,&$childArray){ foreach($arr as $key => $value){ if($key === 'attribute') continue; if(is_array($value)) collectIDs($value,$childArray); else if($key == 'id') $childArray[] = $value; } } collectIDs($array,$childArray); print_r($childArray);