Cumulative sum by group

[Godfrey Smith]

I have a dataset with grouped by a particular variable. The number of observations (rows) in each group ranges from 3 to 20. I want to first sort by group and date, and then perform a cumulative sum over one of the variables, but by group: In each group, I want to sum all previous values of the variable in that group, and then record this rolling or cumulative sum as another variable. I have no idea how to do this in Stata - please help.

[Nick Cox]

Please study and act on http://www.statalist.org/forums/help#stata

. webuse grunfeld

. bysort company (year) : gen cum_invest = sum(invest)

. l company year *invest if inlist(company, 1, 2), sepby(company)

     +------------------------------------+
     | company   year   invest   cum_in~t |
     |------------------------------------|
  1. |       1   1935    317.6      317.6 |
  2. |       1   1936    391.8      709.4 |
  3. |       1   1937    410.6       1120 |
  4. |       1   1938    257.7     1377.7 |
  5. |       1   1939    330.8     1708.5 |
  6. |       1   1940    461.2     2169.7 |
  7. |       1   1941      512     2681.7 |
  8. |       1   1942      448     3129.7 |
  9. |       1   1943    499.6     3629.3 |
 10. |       1   1944    547.5     4176.8 |
 11. |       1   1945    561.2       4738 |
 12. |       1   1946    688.1     5426.1 |
 13. |       1   1947    568.9       5995 |
 14. |       1   1948    529.2     6524.2 |
 15. |       1   1949    555.1     7079.3 |
 16. |       1   1950    642.9     7722.2 |
 17. |       1   1951    755.9     8478.1 |
 18. |       1   1952    891.2     9369.3 |
 19. |       1   1953   1304.4    10673.7 |
 20. |       1   1954   1486.7    12160.4 |
     |------------------------------------|
 21. |       2   1935    209.9      209.9 |
 22. |       2   1936    355.3      565.2 |
 23. |       2   1937    469.9     1035.1 |
 24. |       2   1938    262.3     1297.4 |
 25. |       2   1939    230.4     1527.8 |
 26. |       2   1940    361.6     1889.4 |
 27. |       2   1941    472.8     2362.2 |
 28. |       2   1942    445.6     2807.8 |
 29. |       2   1943    361.6     3169.4 |
 30. |       2   1944    288.2     3457.6 |
 31. |       2   1945    258.7     3716.3 |
 32. |       2   1946    420.3     4136.6 |
 33. |       2   1947    420.5     4557.1 |
 34. |       2   1948    494.5     5051.6 |
 35. |       2   1949    405.1     5456.7 |
 36. |       2   1950    418.8     5875.5 |
 37. |       2   1951    588.2     6463.7 |
 38. |       2   1952    645.5     7109.2 |
 39. |       2   1953      641     7750.2 |
 40. |       2   1954    459.3     8209.5 |
     +------------------------------------+

[Godfrey Smith]

Thank you very much. I can do this kind of stuff in Python, R and Matlab etc, but Stata is a bit foreign to me..

[Godfrey Smith]

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