Patrick Sturgis
>
> I have the following problem:
>
> I have data on individuals indexed by a unique identifier, SERNO. In
> addition to SERNO, I have a vector of variables Z which are
> measurements
> taken on each individual at time t. Lastly, I have a
> variable SERNO2 which,
> for each case, gives the value of SERNO for a matched case
> in the data set.
> What I wish to do is create a second vector of variables,
> X, which copy the
> values of Z for the case indexed by SERNO2 to each value of
> SERNO. Any
> suggestions?
>
I assume that each value of -serno- occurs just once.
There are various ways to check this, e.g. -isid-,
-duplicates-.
Here is a rather tedious approach. Something more
elegant is probably possible.
+---------------------------+
| serno z1 z2 serno2 |
|---------------------------|
1. | 11 6 11 14 |
2. | 12 7 12 13 |
3. | 13 8 13 13 |
4. | 14 9 14 12 |
+---------------------------+
Set up copies, initially missing:
foreach v of var z* {
qui gen c`v' = .
}
Get an observation number variable (serno
may already be that)
gen long obsno = _n
With -levels- from SSC,
levels serno2, local(levels)
foreach l of local levels {
su obsno if serno == `l', meanonly
foreach v of var z* {
qui replace c`v' = `v'[`r(min)'] if serno2 == `l'
}
}
That is, the look-up is done by finding
the observation number for each serial number.
l
+----------------------------------------------+
| serno z1 z2 serno2 cz1 cz2 obsno |
|----------------------------------------------|
1. | 11 6 11 14 9 14 1 |
2. | 12 7 12 13 8 13 2 |
3. | 13 8 13 13 8 13 3 |
4. | 14 9 14 12 7 12 4 |
+----------------------------------------------+
A linked FAQ has just gone up at
http://www.stata.com/support/faqs/data/foreach.html
which in turn supersedes
http://www.stata.com/support/faqs/data/for.html
Ernest Berkhout suggested that the latter should be updated in
a Statalist posting on 24 February.
Nick
[email protected]
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