cumulative sum betwee 1 and 2?

[River Huang]

Dear All, I find this question here (in Chinese). The data set is:

* Example generated by -dataex-. For more info, type help dataex
clear
input float(A B C)
0 0  0
1 2  2
0 4  6
0 5 11
0 3 14
2 0  0
0 0  0
0 0  0
1 3  3
0 6  9
0 7 16
2 0  0
end

A and B are the raw data, and C is the desired result. The purpose is to calculate the cumulative sum of B, starting from A=1 to A=2 for each segment. Any suggestions are highly appreciated.

[Maarten Buis]

clear
input byte(A B C)
0 0  0
1 2  2
0 4  6
0 5 11
0 3 14
2 0  0
0 0  0
0 0  0
1 3  3
0 6  9
0 7 16
2 0  0
end

gen order = _n
gen id = sum(A==1) if sum(A==1) != sum(A==2)
bys id (order) : gen wanted = sum(B) if !missing(id)
sort order
list, sepby(id)

[Nick Cox]

Here's another way to think about it, which will extend fairly painlessly if #1 is really a stalking-horse for a question on panel data.. tsspell is from SSC.

clear
input byte(A B C)
0 0  0
1 2  2
0 4  6
0 5 11
0 3 14
2 0  0
0 0  0
0 0  0
1 3  3
0 6  9
0 7 16
2 0  0
end

gen t = _n 
tsset t 

tsspell, fcond(A > 0) 

bysort _spell (_seq) : gen wanted = sum(B) if A[1] == 1 

sort t 

list, sepby(_spell)  

     +-------------------------------------------------+
     | A   B    C    t   _spell   _seq   _end   wanted |
     |-------------------------------------------------|
  1. | 0   0    0    1        0      0      0        . |
     |-------------------------------------------------|
  2. | 1   2    2    2        1      1      0        2 |
  3. | 0   4    6    3        1      2      0        6 |
  4. | 0   5   11    4        1      3      0       11 |
  5. | 0   3   14    5        1      4      1       14 |
     |-------------------------------------------------|
  6. | 2   0    0    6        2      1      0        . |
  7. | 0   0    0    7        2      2      0        . |
  8. | 0   0    0    8        2      3      1        . |
     |-------------------------------------------------|
  9. | 1   3    3    9        3      1      0        3 |
 10. | 0   6    9   10        3      2      0        9 |
 11. | 0   7   16   11        3      3      1       16 |
     |-------------------------------------------------|
 12. | 2   0    0   12        4      1      1        . |
     +-------------------------------------------------+

[River Huang]

Dear Maarten, Thanks for this helpful suggestion.

[River Huang]

Dear Nick, Thanks for this helpful suggestion.