I am working on a simulation procedure, which randomly permutes
all variables in a varlist before each run (optionally permutes
groups of variables together).
Given original variable dtsim20, I would have thought that the
the two following command sequences would yield the same result,
because my understanding of -replace- was that it works on a
temp copy of the variable, which will not be replaced before
the very end of the -replace- procedure.
[see the full, but very basic example at the end of this post]
1. The "correct" command sequence(?)
. clonevar _dtsim20 = dtsim20
. replace _dtsim20 = dtsim20[dtrank] if tag
2. Incorrect, because of [some sort of circular ref.]?
. clonevar wrong = dtsim20
. replace wrong = wrong[dtrank] if tag
Question:
Could someone please explain exactly why (2) doesn't work?
I guess that I will go with (1), unless someone has a more
clever idea? The only reason I'm asking is that I now have
to do quite a lot of clone/replace/drop/rename in my procedure.
Thanks in advance.
/Jesper K. Hansen
---- begin simple example ----
. sort dtsim20
. mark tag if indexnot(dtsim20,"?") != 0
. set seed 123586
. egen long dtrank = rank(uniform()) if tag , unique
. clonevar _dtsim20 = dtsim20
. replace _dtsim20 = dtsim20[dtrank] if tag
(12 real changes made)
. clonevar wrong = dtsim20
. replace wrong = wrong[dtrank] if tag
(7 real changes made)
. list dtsim20 _dtsim20 wrong dtrank tag
+-------------------------------------------+
| dtsim20 _dtsim20 wrong dtrank tag |
|-------------------------------------------|
1. | + - - 17 1 |
2. | + - - 15 1 |
3. | + + + 3 1 |
4. | + - - 23 1 |
5. | + - - 19 1 |
|-------------------------------------------|
6. | + + - 4 1 |
7. | + - - 28 1 |
8. | + - - 12 1 |
9. | - - - 18 1 |
10. | - + - 2 1 |
|-------------------------------------------|
11. | - - - 30 1 |
12. | - - - 9 1 |
13. | - + - 5 1 |
14. | - - - 24 1 |
15. | - - - 16 1 |
|-------------------------------------------|
16. | - - - 20 1 |
17. | - - - 27 1 |
18. | - - - 22 1 |
19. | - - - 21 1 |
20. | - - - 14 1 |
|-------------------------------------------|
21. | - + - 7 1 |
22. | - - - 25 1 |
23. | - - - 26 1 |
24. | - - - 13 1 |
25. | - + - 6 1 |
|-------------------------------------------|
26. | - + - 8 1 |
27. | - - - 10 1 |
28. | - - - 29 1 |
29. | - + - 1 1 |
30. | - - - 11 1 |
+-------------------------------------------+
---- end simple example ----
-- Jesper Kj�r Hansen
mailto:[email protected]
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