# Re: st: copy value within group

 From "Tim Wade" To statalist@hsphsun2.harvard.edu Subject Re: st: copy value within group Date Mon, 23 Oct 2006 09:50:32 -0400

```I usually use a different approach for these types of problems:

. input id x

id          x
1. 1 1
2. 1 .
3. 1 .
4. 2 2
5. 2 .
6. 2 .
7. 3 3
8. 3 .
9. 3 .
10. 3 .
11. 3 .
12. 4 4
13. 4 .
14. end

. qui bysort id (x): replace x=x[1]

. list

+--------+
| id   x |
|--------|
1. |  1   1 |
2. |  1   1 |
3. |  1   1 |
4. |  2   2 |
5. |  2   2 |
|--------|
6. |  2   2 |
7. |  3   3 |
8. |  3   3 |
9. |  3   3 |
10. |  3   3 |
|--------|
11. |  3   3 |
12. |  4   4 |
13. |  4   4 |
+--------+

On 10/23/06, frakt@bu.edu <frakt@bu.edu> wrote:
```
```frequently, yet I have never been happy about how I do it.  I've always
wondered if there was another way.

*Fact*: In my data there exists a variable, x, with the following
property (known by construction or verified with an -assert-).  Within
each group of observations identified by a unique id (call the variable
id), x is missing for all but one observation.

*Operation*: I want to assign the single nonmissing value of x to all
missing values of x within the group.  That is, when I'm done, x is
nonmissing for all observations and constant within id.  This  constant
value of x (within id) remains unchanged for the original nonmissing
values of x.

*My Solution*: Usually I accomplish this with something like:

bysort id: egen t = mean(x) //other -egen- commands work, like -max()-//
replace x = t drop t

*Comment*: This works because I choose an -egen- command that ignores
code later, it is hard to tell what I'm really doing since my motivation
is not to compute a mean or max, per se, but just to execute
a sort of copy operation within group.  What would be nice is if there
were a command named copy() (or something clear) that (1) verified the
properties I require (see "Fact" above) and then (2) did the operation
I want (see "Operation" above).  Even a more transparent way of just doing
(2) (and not (1)) would be an improvement.  I'm not skilled enough to
easily write such a command.  Perhaps there is such a command or some
other way to do what I want that is more transparent than my solution.
Any suggestions?

Thanks.

*
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```
```*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
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*   http://www.ats.ucla.edu/stat/stata/
```