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st: Updating master dataset with a transation dataset


From   Alice W Muehlhof <muehlhof@Princeton.EDU>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Updating master dataset with a transation dataset
Date   Tue, 14 Mar 2006 07:57:16 -0500

Hi, 
I am relatively new to Stata, although I have programming experience in SAS
and C. 
This is what I would like to do, but I cannot figure out how to do it in
Stata:

    1. My master dataset has hundreds of variables, two of which, var1 and
var2 I 
	combine to use as a unique identifier of each record.

    2. My second dataset, the transaction dataset, has 4 variables: two of
them 
       are the same two as in the master dataset, var1 and var2. They are
not unique 
       identifiers on this dataset.
        a. The third variable in the transaction dataset, (var3), contains
the name 
	   of a variable in the master dataset which is to be updated. This
variable 
	   name is different from record to record on the transaction
dataset. 
        b. The fourth variable, var4, contains the data that is to update
var3 on 
	   the master dataset.
 

Ex: I would match record from transaction dataset with master dataset record
on var1 and var2. 
Then I would look at the contents of the var3 on the transaction dataset
which
would tell me the name of the variable that needed to updated on the master
dataset. Var4 
on the transaction dataset would tell me what the contents of this updated
variable is to be.

It is possible to have several records in the transaction dataset all with
the same unique 
identifier, instructing the system to update different variables on the same
record of the 
master dataset.

Now I know that I can just create a series of replace varname with the
contents of var4
 statements and copy and paste this data into a do-file, and run it that 
way. 

But that is not very efficient, and I need to do this over and over again,
so if 
there is a way I could read the transaction dataset, then retrieve the
appropriate 
record from the master dataset, update the specified variable with it's
contents 
from var4, that would be better.
 
Is there anyway I can do this in Stata?
 
Thank you so much for your help.
 
Alice

Alice Muehlhof
Research Assistant
Woodrow Wilson School
Princeton University

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