First, note that
if shift == -1 {
means
if shift[1] == -1 {
which is probably why you are not getting the results you expect.
There is a big difference between the -if- command and the -if- qualifier.
This has been the focus of several recent threads on this list, including one started by Ashim Kapoor. See also the FAQ
FAQ . . . . . . . . . . . . . . . . . . . . . if command vs. if qualifier
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Wernow
6/00 I have an if command in my program that only seems
to evaluate the first observation, what's going on?
http://www.stata.com/support/faqs/lang/ifqualifier.html
Also, note that (e.g.)
replace flow= (-1*`cap')
-replace-s in _all observations.
You can combine two or more -if-s. You just use as many conditions as are needed together with whatever operators are needed.
. sysuse auto, clear
. list foreign rep78 if foreign == 1 & rep78 == 4
+-----------------+
| foreign rep78 |
|-----------------|
55. | Foreign 4 |
56. | Foreign 4 |
58. | Foreign 4 |
59. | Foreign 4 |
62. | Foreign 4 |
|-----------------|
63. | Foreign 4 |
70. | Foreign 4 |
72. | Foreign 4 |
73. | Foreign 4 |
+-----------------+
. list foreign rep78 if foreign == 1 | rep78 == 4
+------------------+
| foreign rep78 |
|------------------|
5. | Domestic 4 |
15. | Domestic 4 |
24. | Domestic 4 |
29. | Domestic 4 |
30. | Domestic 4 |
|------------------|
33. | Domestic 4 |
35. | Domestic 4 |
38. | Domestic 4 |
47. | Domestic 4 |
53. | Foreign 5 |
|------------------|
54. | Foreign 3 |
55. | Foreign 4 |
56. | Foreign 4 |
57. | Foreign 5 |
58. | Foreign 4 |
|------------------|
59. | Foreign 4 |
60. | Foreign 3 |
61. | Foreign 5 |
62. | Foreign 4 |
63. | Foreign 4 |
|------------------|
64. | Foreign . |
65. | Foreign 3 |
66. | Foreign 5 |
67. | Foreign 5 |
68. | Foreign 5 |
|------------------|
69. | Foreign 5 |
70. | Foreign 4 |
71. | Foreign 5 |
72. | Foreign 4 |
73. | Foreign 4 |
|------------------|
74. | Foreign 5 |
+------------------+
My impression is that you need -if- qualifiers, but you are using -if- commands. Only very rarely in practice does an -if- command pivot on a variable's value.
On a minor detail, negation
replace flow= -`cap'
is even easier than multiplying by -1.
Nick
[email protected]
Linn Renée Naper
I am trying to program a "double if-sentence" in Stata.
Is this possible? And what do I do wrong here?
Here is what I write. The results is that Stata
only performs the commands after the second "else":
replace flow=`cable_cap'.
if shift==-1 {{
if (flow[_n-1] + `cap')<`add' {
replace flow= (-1*`cap')
}
else {
replace flow=flow[_n-1]-`add'
}
}
else {
if (flow[_n-1] - `cap')>`add' {
replace flow=`cap'
}
else {
replace flow=flow[_n-1]+`add'
}
}
I thus try to write a command where the
executed command if the result (if shift==-1) is true also
includes an if-formulation, and the same with
the executed command in the case where
the result of the initial criterion is false.
If the shift value is -1, what I do with the
variable flow depends on whether the
sum (flow[_n-1]+`cap') is larger or smaller than
the value given in `add'. Similarly, if the shift variable
isn't -1 but 1, what I do with flow depends on
the sum (flow[_n-1]-`cap') and whether this sum
is smaller or larger than the value given by `add'.
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