According to the first column group, after the grouping: descending order according to the third column value again, if the second column of the same need to accumulate the value of the third column, such as data is as follows:

A, A, 3
B, c, 4
A, b, 5
D, a, 6
A, A, 6
D, b, 5
B, d, 2
After the statistics became:

A, A, 9
A, b, 5
B, c, 4
B, d, 2
D, a, 6
D, b, 5
Could you tell me the warrior, this how to do? Grateful! Spark core or spark SQL implementation can be