calculate a running sum, with value reset when a contion is hit

Question

Hello,

I'm trying to add a column called csum which would calculate a running sum of days with type: 'm', but ignore days if the type is 'v',
the calculation will end until when a row with the type 'o' is hit. Then the running sum will be reset and start over again.

id days type csum
1 30 v 0
2 25 m 25
3 30 v 25
4 30 m 55
5 25 m 80
6 30 o 110
7 30 v 0
8 5 m 5
9 10 o 15
10 20 v 0
10 10 m 10
11 15 v 10
12 10 o 20
13 15 m 15
14 10 m 25
15 15 v 25
16 10 o 35

Can some one help or give me hint please?

Thanks,

Leon

Answer 1

To calculate this, you need to find the id 1 greater than that of the previous 'o' row, or just 1 if no 'o's happened yet. Next it is a straightforward conditional sum for non-'v's between that id and the current row.