compare and count from two tables using laravel

id  sm_id  to_id
1   3      2
2   4      1
3   3      3
4   3      2
5   3      3
6   4      1

How can I count how many occurences of a to_id an sm_id has?

I have two inputs, first sm_id and second to_id, I want to count occurence of values based on inputs.

Expected result for sm_id = 4 and to_id = 1 would be 2

Here's the code I tried

$us = \DB::table('mgs')
                 ->where('sm_id', '=', DB::raw('to_id'))
        ->where('to_id', '=', DB::raw('sm_id'))
                 ->groupBy('sm_id')
                 ->count();

      print_r($us);die;

via Naresh Verma