I have data that looks something like:
n year y
1 2000
1 2000
1 2001
1 2002 6
1 2002 6
1 2003 9
2 2000
2 2000
2 2001
2 2002 1
2 2002 9
2 2003 4
3 2000
3 2001
3 2002 3
3 2002 3
3 2003 5
3 2003 5
4 1999
4 2000
4 2001
4 2002
4 2002 4
How can I fill in the y value for all years before 2002 with the y value corresponding to the ~first~ observation of 2002 - and do this by n?
For example, for n==2, the first y value of year==2002 is 1. Thus, I would want to fill in the three y values of years 2000 (2) and 2001 (1) with 1. The new dataset would be:
n year y
1 2000 6
1 2000 6
1 2001 6
1 2002 6
1 2002 6
1 2003 9
2 2000 1
2 2000 1
2 2001 1
2 2002 1
2 2002 9
2 2003 4
3 2000 3
3 2001 3
3 2002 3
3 2002 3
3 2003 5
3 2003 5
4 1999
4 2000
4 2001
4 2002
4 2002 4
Note that the years before 2002 for n==4 did not get filled in because the first observation where year==2002 is blank.
I think that a solution may be along the lines of:
bysort n: gen temp = y[1] if year==2002
replace y = temp if year<2002
drop temp
But I am not sure about the first line.
答案 0 :(得分：1)
One (perhaps inelegant) solution:
sort n year, stable // [1]
gen y2 = y
by n year: gen _y = y2[1] if year == 2002 // [2]
egen _y2 = max(_y), by(n) // [3]
replace y2 = _y2 if year < 2002 // [4]
drop _*
li, sepby(n) noobs
yielding:
+-------------------+
| n year y y2 |
|-------------------|
| 1 2000 . 6 |
| 1 2000 . 6 |
| 1 2001 . 6 |
| 1 2002 6 6 |
| 1 2002 6 6 |
| 1 2003 9 9 |
|-------------------|
| 2 2000 . 1 |
| 2 2000 . 1 |
| 2 2001 . 1 |
| 2 2002 1 1 |
| 2 2002 9 9 |
| 2 2003 4 4 |
|-------------------|
| 3 2000 . 3 |
| 3 2001 . 3 |
| 3 2002 3 3 |
| 3 2002 3 3 |
| 3 2003 5 5 |
| 3 2003 5 5 |
|-------------------|
| 4 1999 . . |
| 4 2000 . . |
| 4 2001 . . |
| 4 2002 . . |
| 4 2002 4 4 |
+-------------------+
Notes:
[1] The stable option preserves the ordering of y.
[2] Generates _y equal to the first observation where year == 2002 only. Note that you need by n year or else y[1] is the first observation of the n group even when year != 2002 (but present only for observations where year == 2002).
[3] Fills in _y across the n group.
[4] Replaces y2 for years earlier than 2002.
答案 1 :(得分：1)
mipolate提供“向后”插值，如下所示：
. ssc inst mipolate
. bysort n: mipolate y year, gen(y2) backward
. l
+-------------------+
| n year y y2 |
|-------------------|
1. | 1 2000 . 6 |
2. | 1 2000 . 6 |
3. | 1 2001 . 6 |
4. | 1 2002 6 6 |
5. | 1 2002 6 6 |
|-------------------|
6. | 1 2003 9 9 |
7. | 2 2000 . 5 |
8. | 2 2000 . 5 |
9. | 2 2001 . 5 |
10. | 2 2002 1 5 |
|-------------------|
11. | 2 2002 9 5 |
12. | 2 2003 4 4 |
13. | 3 2000 . 3 |
14. | 3 2001 . 3 |
15. | 3 2002 3 3 |
|-------------------|
16. | 3 2002 3 3 |
17. | 3 2003 5 5 |
18. | 3 2003 5 5 |
19. | 4 1999 . 4 |
20. | 4 2000 . 4 |
|-------------------|
21. | 4 2001 . 4 |
22. | 4 2002 . 4 |
23. | 4 2002 4 4 |
+-------------------+
我提到这一点是因为对这个问题感兴趣的其他人可能会感兴趣。这里的关键是首先对同一标识符和年份的多个观察值进行平均，这不是您想要的。
你问题的特定版本是高度脆弱，因为不知怎的，你知道几个的第一个值是要使用的那个，但是你向我们展示的数据中没有任何标记是什么或为什么。对n year上的数据进行排序，以及首先出现的各种副本中的哪一个可能会发生变化！这是数据管理的危险情况。