RecursiveIteratorIterator

  $a = array();

        // Values inside of ArrayObject instances will be changed correctly, values
        // inside of plain arrays won't
        $a[] = array(new ArrayObject( range( 100, 200, 100 ) ),
            new ArrayObject( range( 200, 100, -100 ) ),
            range( 100, 200, 100 ));
        $a[] = new ArrayObject( range( 225, 75, -75 ) );

        // The array has to be
        //     - converted to an ArrayObject or
        //     - returned via $it->getArrayCopy()
        // in order for this field to get handled properly
        $a[] = 199;

        // These values won't be modified in any case
        $a[] = range( 100, 200, 50 );

        // Comment this line for testing
        $a = new ArrayObject( $a );

        $it = new RecursiveIteratorIterator( new RecursiveArrayIterator( $a ) );

        foreach ( $it as $k => $v ) {
            // getDepth() returns the current iterator nesting level
            echo $it->getDepth() . ': ' . $it->current();

            if ( $v < 200 ) {
                echo "\ttrue";

                // This line is equal to:
                //     $it->getSubIterator($it->getDepth())->offsetSet($k, 0);
                $it->getInnerIterator()->offsetSet( $k, 0 );
            }

            echo ($it->current() == 0) ? "\tchanged" : '';
            echo "\n";
        }

        // In this context, there's no real point in using getArrayCopy() as it only
        // copies the topmost nesting level. It should be more obvious to work with $a
        // itself
        print_r( json_decode( json_encode( $a ), TRUE ) );

        //print_r($it->getArrayCopy());