st: assertky available on SSC

[David Kantor <kantor.d@att.net>]

To all Statalisters:
I want to let you all know that my program -assertky- is available on 
SSC, thanks to Kit Baum.

This is a very simple little program but may be very useful.  It 
merely sorts the dataset, and asserts that the sort variables 
uniquely identify all observations, which also means that the sort 
order is uniquely determined.  This can be useful in in preparation 
for a -merge- or for certain -by- operations. The latter type of 
situation would be...
 by varlist1 (varlist2): ...
where you want to be sure that the combination of varlist1 and 
varlist2 assure a unique sort.  (This construct by itself does not 
assure a unique sort; I am not aware of any enhancements that may 
have come along in Stata 9, regarding this matter.)

The functionality can be replicated with -isid ... , sort missok-, 
but assertky may be easier to use.  There are also options for 
identifying key violations -- finding the problem cases when the 
assertion fails.

I hope this is useful.
--David Kantor

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