protected function applyStepping( $range, $step )
    {
        if ( $step === false || $step === 1 )
        {
            return $range;
        }

        foreach ( $range as $value => $tmp )
        {
            if ( ( $value % $step ) !== 0 )
            {
                unset( $range[$value] );
            }
        }
        return array_values( $range );
    }