Spark groupby过滤器对每个城市的前3篇文章进行排序

Question

我有一个表数据，如下所示：

+-----------+--------+-------------+
| City Name |  URL   |  Read Count |
+-----------+--------+-------------+
| Gurgaon   |  URL1  |  3          |
| Gurgaon   |  URL3  |  6          |
| Gurgaon   |  URL6  |  5          |
| Gurgaon   |  URL4  |  1          |
| Gurgaon   |  URL5  |  5          |
| Delhi     |  URL3  |  4          |
| Delhi     |  URL7  |  2          |
| Delhi     |  URL5  |  1          |
| Delhi     |  URL6  |  6          |
| Punjab    |  URL6  |  5          |
| Punjab    |  URL4  |  1          |
| Mumbai    |  URL5  |  5          |
+-----------+--------+-------------+

我希望看到一些东西，如->前3阅读文章(如果存在)每个城市

+-----------+--------+--------+
| City Name |  URL   |  Count |
+-----------+--------+--------+
| Gurgaon   |  URL3  |      6 |
| Gurgaon   |  URL6  |      5 |
| Gurgaon   |  URL5  |      5 |
| Delhi     |  URL6  |      6 |
| Delhi     |  URL3  |      4 |
| Delhi     |  URL1  |      3 |
| Punjab    |  URL6  |      5 |
| Punjab    |  URL4  |      1 |
| Mumbai    |  URL5  |      5 |
+-----------+--------+--------+

我正在开发Spark 2.0.2，Scala 2.11.8