st: A Problem on generating a variable using --appended-dataset

[Asgar Khademvatani <akhademv@ucalgary.ca>]

Dear All,

Basically, I am estimating a cost model using time series dataset over 
1958-2000. Then, I have appended a new observation over 2001-2050 to my 
master dataset in the Stata memory, using--append-- command. I want to 
generate some new variables defined based on functions upon estimated 
coefficient and the other variables, I want generate these variables 
only over 2001-2050 during the same period of new using 
observation.Actually, I already tried --gen-- command but it only 
generate the variables over master dataset period over 1958-2000 NOT 
over 2001-2050. In doing so, I am going to write a --forvalues-- loop to 
do so. But the variables only are generated at one single 
observation,say only 2001, and it is re-extended over other years with 
the same values . For example, my written loop and the stata results are 
given as:
A Sample Loop:

forvalues i = 44/93 {
    gen X = _b[le_sg] + _b[lple_sg]*(plpl_sg[`i']) + 
_b[lpme_sg]*(plpm_sg[`i']) + _b[lek_neg_sg]*(plk_sg[`i']) + 
_b[let_sg]*(pt[`i'])
    list  X
}


The Stata Output:

do "C:\DOCUME~1\ASGARK~1\LOCALS~1\Temp\STD0i000000.tmp"

.  1.  forvalues i = 44/93 {
 2.      gen X =_b[le_sg] + _b[lple_sg]*(plpl_sg[`i']) + 
_b[lpme_sg]*(plpm_sg[`i']) + _b[lek_neg_sg]*(plk
> _sg[`i']) + _b[let_sg]*(pt[`i'])
 3.      list  X
 4. }        
44

    +-----------+
    |       X
    |-----------|
 1. | -7.730469 |
 2. | -7.730469 |
 3. | -7.730469 |
 4. | -7.730469 |
 5. | -7.730469 |
    |-----------|
 6. | -7.730469 |
 7. | -7.730469 |
 8. | -7.730469 |
 9. | -7.730469 |
10. | -7.730469 |
    |-----------|
11. | -7.730469 |
12. | -7.730469 |
13. | -7.730469 |
14. | -7.730469 |
15. | -7.730469 |
    |-----------|
16. | -7.730469 |
17. | -7.730469 |
18. | -7.730469 |
19. | -7.730469 |
20. | -7.730469 |
    |-----------|
21. | -7.730469 |
22. | -7.730469 |
23. | -7.730469 |
24. | -7.730469 |
25. | -7.730469 |
    |-----------|
26. | -7.730469 |
27. | -7.730469 |
28. | -7.730469 |
29. | -7.730469 |
30. | -7.730469 |
    |-----------|
31. | -7.730469 |
32. | -7.730469 |
33. | -7.730469 |
34. | -7.730469 |
35. | -7.730469 |
    |-----------|
36. | -7.730469 |
37. | -7.730469 |
38. | -7.730469 |
39. | -7.730469 |
40. | -7.730469 |
    |-----------|
41. | -7.730469 |
42. | -7.730469 |
43. | -7.730469 |
44. | -7.730469 |
45. | -7.730469 |
    |-----------|
46. | -7.730469 |
47. | -7.730469 |
48. | -7.730469 |
49. | -7.730469 |
50. | -7.730469 |
    |-----------|
51. | -7.730469 |
52. | -7.730469 |
53. | -7.730469 |
54. | -7.730469 |
55. | -7.730469 |
    |-----------|
56. | -7.730469 |
57. | -7.730469 |
58. | -7.730469 |
59. | -7.730469 |
60. | -7.730469 |
    |-----------|
61. | -7.730469 |
62. | -7.730469 |
63. | -7.730469 |
64. | -7.730469 |
65. | -7.730469 |
    |-----------|
66. | -7.730469 |
67. | -7.730469 |
68. | -7.730469 |
69. | -7.730469 |
70. | -7.730469 |
    |-----------|
71. | -7.730469 |
72. | -7.730469 |
73. | -7.730469 |
74. | -7.730469 |
75. | -7.730469 |
    |-----------|
76. | -7.730469 |
77. | -7.730469 |
78. | -7.730469 |
79. | -7.730469 |
80. | -7.730469 |
    |-----------|
81. | -7.730469 |
82. | -7.730469 |
83. | -7.730469 |
84. | -7.730469 |
85. | -7.730469 |
    |-----------|
86. | -7.730469 |
87. | -7.730469 |
88. | -7.730469 |
89. | -7.730469 |
90. | -7.730469 |
    |-----------|
91. | -7.730469 |
92. | -7.730469 |
93. | -7.730469 |
94. | -7.730469 |
    +-----------+
X already defined
r(110);

end of do-file


As you see in the above, X variable is generated only in 2001 and it is 
repeated over next years with the same value. I am not sure what is 
wrong with my loop.  May somebody please help me out on this matter and 
tell me what is wrong with that? Otherwise, I am just wondering that is 
there another way other than writing a loop for generating the variables 
over 2001-2050?

Thank you in advance for any help.

Asgar Kh.
University of Calgary-Canada
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