How to Sanitize data in FilterInterface CI4

Hi,

Can somebody tell me how to use FilterInterface in modifying request before using it in the Controller? I want to sanitize or to remove unwanted characters in the data before using it in my Controller.

Here is the sample of my code: 

Filter:

PHP Code:

namespace App\Filters;

use CodeIgniter\HTTP\RequestInterface;
use CodeIgniter\HTTP\ResponseInterface;
use CodeIgniter\Filters\FilterInterface;

class SanitizeFields implements FilterInterface
{

    protected $session;

    public function before(RequestInterface $request, $arguments = null)
    {
        $request->getVar('number_only', FILTER_SANITIZE_NUMBER_INT);
    }

    public function after(RequestInterface $request, ResponseInterface $response, $arguments = null)
    {
        // Do something here
    }
} 


Controller: 

PHP Code:

//controller
public function getData()
{
    echo $this->request->getVar('number_only');
} 


Is it possible to sanitize the value of number_only variable from "123abc456" to "123456"? 

Thank you!

PHP Code:

// Check to see if the variable is an integer
if (filter_var($this->request->getVar('number_only'), FILTER_VALIDATE_INT) === false)
{
    // ERROR!  
}
else
{
    echo $this->request->getVar('number_only');
} 


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