in array how to pass query for perfect result

 $arr = str_replace('"','', $request->course_id);
  $arr = str_replace('"','', $request->stream_id);
    $arr = str_replace('[','', $arr);
    $arr = str_replace(']','', $arr);
    $arr = explode(',',$arr);
      $a = array(College::whereIn('course_id',$arr)->get());
     $b = array(College::whereIn('stream_id',$arr)->get());
    
    $result =  array_merge($arr,$a, $b );
     return $result;

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This is code i done, but not get exact result which i want, i want to filter like when pass id course id 1 and value BCA then show BCA college list, college is 1 table and course is another table and common id in both table is course id, what is exact problem in this code

via Chebli Mohamed