st: Re:Combining forvalues and by

[Kit Baum <baum@bc.edu>]

Pierre a dit:

I am trying to calculate the so-called h index for a large number of
scientists. The h index of a scientist and the highest integer h such
that the scientist has h papers cited at least h times.


As is often the case, no explicit looping over observations is  
necessary nor desirable.

. list,sepby(var1)

     +--------------------------+
     |   var1       var2   var3 |
     |--------------------------|
  1. | GEORGE   10101157      8 |
  2. | GEORGE   12242494     10 |
  3. | GEORGE   11156976     12 |
  4. | GEORGE    9409826     19 |
  5. | GEORGE    7635312     23 |
  6. | GEORGE    7799970     23 |
  7. | GEORGE   11290701     28 |
  8. | GEORGE    8034742     42 |
  9. | GEORGE    8334302     43 |
10. | GEORGE    2656402     74 |
11. | GEORGE    2005819     79 |
12. | GEORGE    2643162    111 |
13. | GEORGE    8943317    127 |
14. | GEORGE    1956405    146 |
15. | GEORGE    9314530    153 |
16. | GEORGE    2404021    204 |
17. | GEORGE    3049620    302 |
18. | GEORGE    2195038    373 |
19. | GEORGE    2476649    393 |
20. | GEORGE    2005809    527 |
21. | GEORGE    6365931    614 |
22. | GEORGE    6365930    670 |
     |--------------------------|
23. |  HENRY   10101157     18 |
24. |  HENRY   12242494     20 |
25. |  HENRY   11156976     22 |
26. |  HENRY    9409826     29 |
27. |  HENRY    7635312     33 |
28. |  HENRY    7799970     33 |
29. |  HENRY   11290701     38 |
30. |  HENRY    8034742     52 |
31. |  HENRY    8334302     53 |
32. |  HENRY    2656402     84 |
33. |  HENRY    2005819     89 |
34. |  HENRY    2643162    121 |
35. |  HENRY    8943317    137 |
36. |  HENRY    1956405    156 |
37. |  HENRY    9314530    163 |
38. |  HENRY    2404021    214 |
39. |  HENRY    3049620    312 |
40. |  HENRY    2195038    383 |
41. |  HENRY    2476649    403 |
42. |  HENRY    2005809    537 |
43. |  HENRY    6365931    624 |
44. |  HENRY    6365930    680 |
     +--------------------------+

. gsort var1 -var3

. by var1: g beat=_n*(var3>=_n)

. by var1: egen h = max(beat)

. by var1: keep if _n==1
(42 observations deleted)

. list var1 h

     +-------------+
     |   var1    h |
     |-------------|
  1. | GEORGE   19 |
  2. |  HENRY   20 |
     +-------------+




Kit Baum, Boston College Economics and DIW Berlin
http://ideas.repec.org/e/pba1.html
An Introduction to Modern Econometrics Using Stata:
http://www.stata-press.com/books/imeus.html


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