Определение количества уникальных пар title и user_id

Необходимо посчитать, сколько разных сочетаний названия события (поле "title") и идентификатора пользователя (поле "user_id") встречается в массиве записей.

{
  "events": [
    {
      "time": "2022-06-17 08:54:03",
      "title": "search",
      "user_id": null,
      "ref": "main",
      "session_id": "a2"
    },
    {
      "time": "2022-06-17 23:19:33",
      "title": "main",
      "user_id": null,
      "ref": null,
      "session_id": "b4"
    },
    {
      "time": "2022-06-20 13:02:44",
      "title": "success",
      "user_id": null,
      "ref": "seats",
      "session_id": "b1"
    },
    {
      "time": "2022-06-20 14:45:43",
      "title": "search_click",
      "user_id": 123,
      "page": "main",
      "session_id": "a1"
    },
    {
      "time": "2022-06-20 14:46:49",
      "title": "main",
      "user_id": 123,
      "ref": null,
      "session_id": "a1"
    },
    {
      "time": "2022-06-17 23:21:31",
      "title": "search",
      "user_id": null,
      "ref": "main",
      "session_id": "b5"
    },
    {
      "time": "2022-06-18 13:02:44",
      "title": "main",
      "user_id": null,
      "ref": "seats",
      "session_id": "c2"
    },
    {
      "time": "2022-06-18 14:47:03",
      "title": "seats",
      "user_id": 123,
      "ref": "search",
      "session_id": "d1"
    },
    {
      "time": "2022-06-18 13:12:41",
      "title": "search",
      "user_id": null,
      "ref": "seats",
      "session_id": "c4"
    },
    {
      "time": "2022-06-20 14:44:01",
      "title": "chat_open",
      "user_id": 123,
      "page": "seats",
      "session_id": "d1"
    },
    {
      "time": "2022-06-20 14:46:32",
      "title": "chat_send_message",
      "user_id": 123,
      "page": "seats",
      "session_id": "d1"
    },
    {
      "time": "2022-06-21 13:12:41",
      "title": "seats",
      "user_id": 34,
      "ref": null,
      "session_id": "c4"
    },
    {
      "time": "2022-06-21 21:14:00",
      "title": "success",
      "user_id": null,
      "ref": null,
      "session_id": "b4"
    }
  ]
}