How do I compare a string array to a numeric array?

dear users of StackOverflow. There is some problem.

Array 1:
array: 3 [▼
   0 => "8"
   1 => "13"
   2 => "15"
]

Array 2:
array: 16 [▼
   0 => 7
   1 => 8
   2 => 9
]

array_diff does not work, because in the first number, in the second string.

Please suggest any ideas for solving the issue. I will be happy with any comment. Many thanks.

via Chebli Mohamed