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st: RE: multiple observations - collapsing a string variable?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: multiple observations - collapsing a string variable?
Date   Fri, 10 Dec 2004 18:22:50 -0000

Something like this might help: 

tostring labno, gen(LABNO) 
bysort individual_id : 
	replace LABNO = LABNO[_n-1] + "\" + LABNO if _n > 2 

Nick 
n.j.cox@durham.ac.uk 

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of 
> Chris Wallace
> Sent: 10 December 2004 11:47
> To: statalist@hsphsun2.harvard.edu
> 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?

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