st: mahaselectunique added to mahapick

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

Hello All,

Thanks to Kit Baum, a new component, mahaselectunique, has been added 
to the mahapick module on SSC.

Every once-in-a-while, someone asks for this, so I have finally made 
it into a program for general use.

mahaselectunique enables you to take the output of mahapick (a set of 
"near" observations, according to a Mahalanobis distance measure) and 
selects unique matches based on a randomized priority.
That is, mahaselectunique would typically follow the use of mahapick 
-- to reduce the resulting data to a unique set -- unique in that a 
given control observation appears only once. It is not unique in that 
a randomization process is used. And there is no optimization either; 
that's another story for another day.

Thanks go to those of you who have been requesting this; most 
recently this includes David Greenwood-Sanches and Paula Arce.

To install:
ssc install mahapick

(There are also some minor updates to some of the existing help files 
therein -- for other components.)

--David

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