unset array keys if key is string

Question

i have array something like this

$arr  = 
    ['0' => 
        ['0' => 'zero', 
         '1' => 'test', 
         '2' =>'testphp',
         'test'=>'zero',
         'test1'=>'test',
         'test2'=>'testphp'],
    '1' => 
        ['0' => 'z', 
         '1' => 'x', 
         '2' =>'c',
         'test'=>'z',
         'test1'=>'x',
         'test2'=>'c']
        ];

and 0,1,2 is this same as test,test1,test2. I need remove keys where is string like test,test1,test2. I know the way

foreach($arr as $a){
   unset($arr['test']);
   unset($arr['test1']);
   unset($arr['test2']);
}

but it is possible find keys without specifying the exact name, because i want only number keys.

Answer 1

A solution would be:

Assuming you know it will only have 2 layers.

 $arr  =
['0' =>
    ['0' => 'zero',
        '1' => 'test',
        '2' =>'testphp',
        'test'=>'zero',
        'test1'=>'test',
        'test2'=>'testphp'],
    '1' =>
        ['0' => 'z',
            '1' => 'x',
            '2' =>'c',
            'test'=>'z',
            'test1'=>'x',
            'test2'=>'c']
];

foreach($arr as $parentKey=>$arrayItem){
    foreach($arrayItem as $key=>$subArrayItem){
        if(!is_int($key)){
            unset($arr[$parentKey][$key]);
        }
    }
}
var_dump($arr);

Why is it though that such arrays have been generated?