Online PHP editor | refs for rIfiJ

<?php $array = [ [ 'case_code_id' => 1, 'parent_id' => 0, 'case_code' => 'Main A', 'sub_codes' => [ [ 'case_code_id' => 3, 'parent_id' => 1, 'case_code' => 'Sub A', 'sub_codes' => [ [ 'case_code_id' => 5, 'parent_id' => 3, 'case_code' => 'Sub Sub A', 'sub_codes' => [] ] ] ], [ 'case_code_id' => 4, 'parent_id' => 1, 'case_code' => 'Sub B', 'sub_codes' => [] ] ] ], [ 'case_code_id' => 2, 'parent_id' => 0, 'case_code' => 'Main B', 'sub_codes' => [] ] ]; function flatten(array $array): array { $result = []; foreach ($array as $v) { $subCode = $v['sub_codes']; unset($v['sub_codes']); array_push( $result, $v, ...flatten($subCode) ); } return $result; } var_export(flatten($array));