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| Title | Setting different observations equal | |
| Author | Jeremy B. Wernow, StataCorp |
Here is a common mistake that is made when attempting to replace an observation of a variable with a different observation from another variable:
. list
+--------------+
| price mpg |
|--------------|
1. | 4,099 22 |
2. | 4,749 17 |
3. | 3,799 22 |
4. | 4,816 20 |
5. | 7,827 15 |
|--------------|
6. | 5,788 18 |
7. | 4,453 26 |
8. | 5,189 20 |
9. | 10,372 16 |
10. | 4,082 19 |
+--------------+
. replace mpg[4] = price[7]
weights not allowed
r(101);
The correct syntax would be to use the in qualifier.
. replace mpg= price[7] in 4
(1 real change made)
. list
+---------------+
| price mpg |
|---------------|
1. | 4,099 22 |
2. | 4,749 17 |
3. | 3,799 22 |
4. | 4,816 4453 |
5. | 7,827 15 |
|---------------|
6. | 5,788 18 |
7. | 4,453 26 |
8. | 5,189 20 |
9. | 10,372 16 |
10. | 4,082 19 |
+---------------+
In programming, you might use macros in place of known values. Observe how the following do-file performs the same task as the above example:
------------------------------------------------------example.do
local x = 7
local i = 4
replace mpg = price[`x'] in `i'
------------------------------------------------------example.do
. list
+--------------+
| price mpg |
|--------------|
1. | 4,099 22 |
2. | 4,749 17 |
3. | 3,799 22 |
4. | 4,816 20 |
5. | 7,827 15 |
|--------------|
6. | 5,788 18 |
7. | 4,453 26 |
8. | 5,189 20 |
9. | 10,372 16 |
10. | 4,082 19 |
+--------------+
. do example.do
. local x = 7
. local i = 4
. replace mpg = price[`x'] in `i'
(1 real change made)
.
end of do-file
. list
+---------------+
| price mpg |
|---------------|
1. | 4,099 22 |
2. | 4,749 17 |
3. | 3,799 22 |
4. | 4,816 4453 |
5. | 7,827 15 |
|---------------|
6. | 5,788 18 |
7. | 4,453 26 |
8. | 5,189 20 |
9. | 10,372 16 |
10. | 4,082 19 |
+---------------+
