Creating a rank that resets on a specific value of a column

Question

My current data looks like this (note that it is sorted on datetime):

+----------------+---------------------+---------+
| CustomerNumber |        Date         | Channel |
+----------------+---------------------+---------+
|      120584446 | 2015-05-22 21:16:05 |    A    |
|      120584446 | 2015-05-25 18:04:16 |    A    |
|      120584446 | 2015-05-25 18:05:25 |    B    |
|      120584446 | 2015-05-28 20:35:09 |    A    |
|      120584446 | 2015-05-28 20:36:01 |    A    |
|      120584446 | 2015-05-28 20:37:02 |    B    |
|      120584446 | 2015-05-29 13:39:00 |    B    |
+----------------+---------------------+---------+
I want to create a rank in hive that splits on cutomer number and whenever the channel is A. It should look like this:

+----------------+---------------------+----------------+------+
| CustomerNumber |          Date       |        Channel | Rank |
+----------------+---------------------+----------------+------+
|      120584446 | 2015-05-22 21:16:05 |    A           |    1 |
|      120584446 | 2015-05-25 18:04:16 |    A           |    1 |
|      120584446 | 2015-05-25 18:05:25 |    B           |    2 |
|      120584446 | 2015-05-28 20:35:09 |    A           |    1 |
|      120584446 | 2015-05-28 20:36:01 |    A           |    1 |
|      120584446 | 2015-05-28 20:37:02 |    B           |    2 |
|      120584446 | 2015-05-29 13:39:00 |    B           |    3 |
+----------------+---------------------+----------------+------+

Answer 1

One approach is to use a cumulative conditional sum to identify the groups and then use row_number() for the ranking:

select t.*,
       row_number() over (partition by CustomerNumber, grp
                          order by date
                         ) as rank
from (select t.*,
             sum(case when channel = 'A' then 1 else 0 end) over
                 (partition by CustomerNumber order by date) as grp
      from t
     ) t;