Allan Reese <[email protected]> correctly noted that
. gen y[rankx] = x
is disallowed. Still, there is a way to achieve the desired result:
. gen i = _n
. sort rankx
. gen y = x[i]
. sort i
Let's try this solution with a little bit of the auto data, creating
new variable -new- equal to mpg, in order. We'll start with,
. sysuse auto
. keep make mpg
. keep in 1/10
. list
+---------------------+
| make mpg |
|---------------------|
1. | AMC Concord 22 |
2. | AMC Pacer 17 |
3. | AMC Spirit 22 |
4. | Buick Century 20 |
5. | Buick Electra 15 |
|---------------------|
6. | Buick LeSabre 18 |
7. | Buick Opel 26 |
8. | Buick Regal 20 |
9. | Buick Riviera 16 |
10. | Buick Skylark 19 |
+---------------------+
. gen i = _n
. sort mpg
. gen new = mpg[i]
. sort i
. list make mpg new
+---------------------------+
| make mpg new |
|---------------------------|
1. | AMC Concord 22 15 |
2. | AMC Pacer 17 16 |
3. | AMC Spirit 22 17 |
4. | Buick Century 20 18 |
5. | Buick Electra 15 19 |
|---------------------------|
6. | Buick LeSabre 18 20 |
7. | Buick Opel 26 20 |
8. | Buick Regal 20 22 |
9. | Buick Riviera 16 22 |
10. | Buick Skylark 19 26 |
+---------------------------+
How the trick works
-------------------
We create an indexing variable i = (1,2,3,...,_N) and then put the
data in the order of mpg (or the indexing variable, or whatever).
The reuslt of that is to permute i. The first value of i is now where
that that observation used to reside. Let's look:
. * picking up from where we left off,
. sort mpg // put the data back in mpg order
. list
+--------------------------------+
| make mpg i new |
|--------------------------------|
1. | Buick Electra 15 5 19 |
2. | Buick Riviera 16 9 22 |
3. | AMC Pacer 17 2 16 |
4. | Buick LeSabre 18 6 20 |
5. | Buick Skylark 19 10 26 |
|--------------------------------|
6. | Buick Century 20 4 18 |
7. | Buick Regal 20 8 22 |
8. | AMC Concord 22 1 15 |
9. | AMC Spirit 22 3 17 |
10. | Buick Opel 26 7 20 |
+--------------------------------+
The Buick Electra was observation 5 in the original ordering. When we
put the data back in the original order, we want -new- to take on the
5th value of mpg, which is to say, mpg[5]. The Buick Riviera used to be
the 9th observation. When we put the data back in order, we want -new-
to take on the 9th value of mpg, which is to say, mpg[9]. Hence,
. gen new = mpg[i]
produces what we want and then it is just a matter of putting the data
back into the original order.
-- Bill
[email protected]
*
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