工作目录里有一个事件文件 data/events.parquet，列为 event_id, user_id, ts, event_type, page。
统计每个用户的购买次数（event_type = 'purchase' 的事件数）。
result必须是一个 LazyFrame：从文件开始就用惰性方式构建查询，不要 collect，判题器会替你 collect。- 只输出至少有一次购买的用户。
输出
列为 user_id, n_purchases，行顺序不限。
LazyFrame 管道
工作目录里的文件 （case base）
data/events.parquet| # | event_idInt64 | user_idInt64 | tsDatetime(time_unit='us', time_zone=None) | event_typeString | pageString |
|---|---|---|---|---|---|
| 1 | 1 | 53 | 2026-06-03 17:57:33 | login | /home |
| 2 | 2 | 53 | 2026-06-04 15:21:00 | visit | /home |
| 3 | 3 | 53 | 2026-06-04 15:22:00 | view | /product/303 |
| 4 | 4 | 53 | 2026-06-04 15:32:04 | add_to_cart | /cart |
| 5 | 5 | 56 | 2026-06-05 23:24:19 | login | /home |
| 6 | 6 | 56 | 2026-06-05 23:29:18 | view | /product/202 |
| 7 | 7 | 56 | 2026-06-05 23:36:15 | view | /product/202 |
| 8 | 8 | 56 | 2026-06-05 23:47:36 | add_to_cart | /cart |
| 9 | 9 | 56 | 2026-06-05 23:56:24 | checkout | /checkout |
| 10 | 10 | 56 | 2026-06-06 19:14:00 | visit | /home |
| 11 | 11 | 56 | 2026-06-06 19:22:53 | view | /product/303 |
| 12 | 12 | 56 | 2026-06-06 19:25:12 | view | /home |
| 13 | 13 | 56 | 2026-06-06 19:28:25 | add_to_cart | /cart |
| 14 | 14 | 29 | 2026-06-07 10:40:01 | login | /home |
| 15 | 15 | 29 | 2026-06-07 10:46:43 | view | /product/303 |
| 16 | 16 | 29 | 2026-06-07 11:04:46 | add_to_cart | /cart |
| 17 | 17 | 29 | 2026-06-07 11:09:25 | checkout | /checkout |
| 18 | 18 | 34 | 2026-06-07 12:57:49 | login | /home |
| 19 | 19 | 34 | 2026-06-07 13:03:57 | view | /product/202 |
| 20 | 20 | 34 | 2026-06-07 13:11:07 | view | /home |
显示前 20 行，共 1500 行
期望输出 （case base，行顺序不限）
| # | user_idInt64 | n_purchasesUInt32 |
|---|---|---|
| 1 | 26 | 6 |
| 2 | 48 | 4 |
| 3 | 39 | 3 |
| 4 | 29 | 3 |
| 5 | 59 | 2 |
| 6 | 45 | 3 |
| 7 | 16 | 2 |
| 8 | 28 | 3 |
| 9 | 57 | 1 |
| 10 | 31 | 2 |
| 11 | 15 | 1 |
| 12 | 22 | 1 |
| 13 | 33 | 1 |
| 14 | 18 | 2 |
| 15 | 21 | 2 |
| 16 | 5 | 1 |
| 17 | 58 | 1 |
| 18 | 56 | 2 |
| 19 | 11 | 4 |
| 20 | 35 | 1 |
| 21 | 17 | 2 |
| 22 | 23 | 1 |
| 23 | 54 | 2 |
| 24 | 25 | 2 |
| 25 | 43 | 1 |
| 26 | 9 | 1 |
| 27 | 3 | 1 |
| 28 | 55 | 1 |
| 29 | 4 | 6 |
| 30 | 42 | 2 |
| 31 | 47 | 7 |
| 32 | 14 | 1 |
| 33 | 50 | 3 |
| 34 | 8 | 2 |
| 35 | 49 | 1 |
| 36 | 7 | 3 |
| 37 | 36 | 4 |
| 38 | 32 | 2 |
| 39 | 20 | 2 |
| 40 | 30 | 1 |
| 41 | 46 | 3 |
| 42 | 34 | 1 |
| 43 | 41 | 4 |
| 44 | 6 | 1 |
| 45 | 60 | 2 |
| 46 | 19 | 1 |
| 47 | 13 | 1 |
| 48 | 12 | 1 |
共 48 行