Something like this might help:
tostring labno, gen(LABNO)
bysort individual_id :
replace LABNO = LABNO[_n-1] + "\" + LABNO if _n > 2
Nick
[email protected]
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of
> Chris Wallace
> Sent: 10 December 2004 11:47
> To: [email protected]
> Subject: st: multiple observations - collapsing a string variable?
>
>
> Short question:
>
> I would like to be able to -collapse- some data concatenating multiple
> values of a string variable, rather than taking some function of a
> numeric variable. Is this at all possible?
>
>
> Longer explanation of why:
>
> I am using a biochemical dataset where each individual has had a blood
> sample analysed for multiple biochemical variables. Each individual
> may has multiple records, each identified by a different labnumber
> (labno), as different variables are measured at different times. So a
> typical record might be (where x represents a non-missing and . a
> missing value):
>
> individual_id labno potassium sodium hdl cholesterol
> 00001 78882 x x . .
> 00001 72010 . . x x
>
> I want to collapse the data so I have a single record:
>
> individual_id potassium sodium hdl cholesterol
> 00001 x x x x
>
> This is fine with "typical" records, as above. But sometimes the same
> test may have been performed twice (either (a) as a check that the lab
> was working ok, or (b) because something seemed wrong about one
> analysis), so there'll be a record like:
>
> individual_id labno potassium sodium hdl cholesterol
> 00002 78882 x x . .
> 00002 72010 . . x x
> 00002 82901 . . y y
>
> where the hdl and cholesterol levels differ. I want to list all such
> records to distinguish between cases (a) and (b). I stored the names
> of all (25) biochemical variables in the local macro allvars and did:
>
>
> log using biochem-multiples, replace
> qui {
> foreach v of local allvars {
> preserve
> keep individual_id `v'
> collapse (min) mn=`v' (max) mx=`v' , by(individual_id)
> noi di "! `v'"
> noi l ind mn mx if mn!=mx
> restore
> }
> }
> log close
> view biochem-multiples.smcl
>
> which lists all the individuals with multiple non-null, differing
> records for any covar. But I would like to also see the labno's for
> these records. I can manually scroll through the log file typing -di
> if ...-, but would like to automate it. I guess what I would love is
> to be able to replace the collapse like above with
>
> keep individual_id labno `v'
> collapse (min) mn=`v' (max) mx=`v' (concatenate, punct("/"))
> labno=labno, by(individual_id)
>
> so that, for individual 00002 I would have in the logfile
>
> 00002 x y 78882/72010/82901
>
> Even better would be
>
> 00002 x y 72010/82901
>
> (listing the labno's only for the observations that are problems).
> But I have no idea how to do this. Can anyone help - perhaps with an
> alternative route altogether?
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
