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st: problem creating unique identifier


From   Christopher Hajzler <chajzler@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: problem creating unique identifier
Date   Sun, 6 Dec 2009 13:47:20 -0600

Dear Statalist,

My version of Stata is doing something quite strange (Version 8.0
intercooled).  I have several variables which are contained in
separate data files, and I want to merge them by creating a unique
identifier for each observation (over which I can sort the data - I
realize it is not strictly necessary to do it this way, but I thought
this method would help avoid errors).  Each observation represents a
city pair (just over 100 cities), and an "item", and in each file I've
created the variable using the following command:
gen newid = 0
replace newid = 1000000*itemid + 1000*cityid1 + cityid2

For some reason Stata will only do a partial job - it seems to be
getting the itemid and cityid1 right when producing newid (the first 4
or 5 digits), and "almost" gets cityid2 right, assigning the correct
values every few observations but then incorrectly allocating the same
value to adjacent observations. For example, one file reads:

newid                itemid       cityid1      cityid2      var1
...
22061006           22             61              6           ...
22061008           22             61              8           ...
22061008           22             61              9           ...
22061008           22             61              7           ...
22061010           22             61              10          ...
22061012           22             61              13          ...
...

I have worked with much larger datasets, so I cannot imagine memory
allocation is an issue. Any other ideas?

Best wishes,
Chris

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