On 9/25/06, FUKUGAWA, N. <[email protected]> wrote:
Dear all,
Suppose we have data as follows,
year var1
1997 14
1997 32
1997 19
1998 18
1998 42
1998 50
1999 3
1999 23
1999 37
we want to keep observations by year if var1 is maximum within
the same year.
year var1
1997 32
1998 50
1999 37
There are two possible approaches, and which you use depends on
whether there are other variables in your data set which you wish to
retain.
1) No other variables need to be retained.
In this instance you can simply -collapse- your dataset...
. list
+-------------+
| year var1 |
|-------------|
1. | 1997 14 |
2. | 1997 32 |
3. | 1997 19 |
4. | 1998 18 |
5. | 1998 42 |
|-------------|
6. | 1998 50 |
7. | 1999 3 |
8. | 1999 23 |
9. | 1999 37 |
+-------------+
. collapse (max) var1, by(year)
. list
+-------------+
| year var1 |
|-------------|
1. | 1997 32 |
2. | 1998 50 |
3. | 1999 37 |
+-------------+
2) Other variables you wish to retain...
. list
+---------------------------+
| year var1 var2 var3 |
|---------------------------|
1. | 1997 14 a .12 |
2. | 1997 32 b .14 |
3. | 1997 19 c .15 |
4. | 1998 18 a .09 |
5. | 1998 42 b .1 |
|---------------------------|
6. | 1998 50 b .16 |
7. | 1999 3 c .11 |
8. | 1999 23 a .12 |
9. | 1999 37 a .1 |
+---------------------------+
. bysort year: egen t = max(var1)
. list
+--------------------------------+
| year var1 var2 var3 t |
|--------------------------------|
1. | 1997 14 a .12 32 |
2. | 1997 32 b .14 32 |
3. | 1997 19 c .15 32 |
4. | 1998 18 a .09 50 |
5. | 1998 42 b .1 50 |
|--------------------------------|
6. | 1998 50 b .16 50 |
7. | 1999 3 c .11 37 |
8. | 1999 23 a .12 37 |
9. | 1999 37 a .1 37 |
+--------------------------------+
. keep if(var1 == t)
(6 observations deleted)
. drop t
. list
+---------------------------+
| year var1 var2 var3 |
|---------------------------|
1. | 1997 32 b .14 |
2. | 1998 50 b .16 |
3. | 1999 37 a .1 |
+---------------------------+
(although I suspect this code could probably be condensed its
hopefully illustrative).
Neil
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