Online PHP editor | refs for jKL9Y

<?php $array = [ 'uid_1' => [ 'sub_1' => [ 'sub_sub_1' => ['id1' => 'val_1', 'id2' => 'val_2'] ], 'sub_2' => [ 'sub_sub_1' => ['id1' => 'val_1', 'id2' => 'val_2'], 'sub_sub_2' => ['id3' => 'val_3', 'id4' => 'val_4'] ] ], 'uid_2' => [ 'sub_1' => [ 'sub_sub_1' => ['id1' => 'val_1', 'id3' => 'val_3'] ], ] ]; foreach ($array as &$uids) { foreach ($uids as &$subs) { $subs['sub_sub_1']['id5'] = 'val_5'; } } var_export($array);