I need to remove all elements from an associative array based on a variable name

I am reading input from the user (in Laravel) and have rules associated to each of those inputs. If the user selects a checkbox (for that specific table), I would like to remove all the rules from the $rules associative array for that table.

To better illustrate, I have created two arrays mimicking the behaviour.

My input array is as follows:

$input = array("TB1_course" => ['0'=>'CHEM 1E03', '1'=>'ENG 1D04'
                            ],  
          "TB1_section" => ['0'=>'CHEM 1E03', '1'=>'ENG 1D04'
                            ], 
          "TB1_checkbox" => "1",
          "TB2_course" => ['0'=>'CHEM 1E03', '1'=>'ENG 1D04'
                            ],
          "TB2_checkbox" => "0"
);

$rules= array(
    'TB1_course.*' => 'required_with',
    'TB1_section.*' =>'required_with',
    'TB2_course.*' =>'required_with'
);

You can see from the input array that TB1_checkbox has a value of 1. If it has a value of 1, I would like to remove all the rules associated with TB1 (i.e. remove the elements in $rules with a key containing 'TB1').

I attempted to do as such, and was partially successful. My code looks like:

foreach ($input as $key=>$value){//go thru every element of the inputs
    if ((strpos($key, 'checkbox')!==false) && $value==1){//if it contains 'checkbox' 
//and checkbox is selected

        $table_name= substr($key, 0,3);//name of table

        //now go thru $rules and remove all elements which contain a word of $table_name

        $rules=array_filter($rules, function($x){
            return strpos($x, $table_name)!==0;//problem lies here
        }, ARRAY_FILTER_USE_KEY);
    }
}

However my code isn't working. The strpos() function is unable to read the $table_name variable, and leads to problems. If I manually pass in a string, it ends up working (i.e. 'TB1' instead of $table_name), but I have to have the flexibility of checking all my tables (so the rules containing 'TB2' have to be removed if "TB2_checkbox" has a value of 1). Is there any way to solve this issue?

Thank you for the help.