st: Create common ID # from several changing ID #s

[Andrea Drechsler <andreamm@wharton.upenn.edu>]

Hello,

I have a dataset of medical providers at the provider-year level.
Each provider has an ID #.  If the provider moves to a new location,
they are assigned a new ID #.  I have two other variables that
sometimes contain providers' previous or future ID #s.  I'm trying to
create a common ID # for each provider so I can track them over time.

For example, I'd like to assign all of the following observations a common ID #:

current_id		other_id1		other_id2
406434166		406434127
406434127		406434166		406414087
406414087		406384157
406384157

Thanks very much in advance!

~ Andrea Drechsler
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