st: RE: Preventing double counting

[Nick Cox <n.j.cox@durham.ac.uk>]

In addition to Brendan's suggestion, you can check consistency like this: 

gen first = min(orig, dest)
gen second = max(orig, dest)
bysort first second : assert _N == 1 if first == second 
by first second: assert _N == 2 if first < second 
by first second : assert netmigration[1] == -netmigration[_N] 

See also 

SJ-8-4  dm0043  . Tip 71: The problem of split identity, or how to group dyads
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q4/08   SJ 8(4):588--591                                 (no commands)
        tip on how to handle dyadic identifiers

Nick 
n.j.cox@durham.ac.uk 

Michael Betz

I have state-to-state migration data that is as follows:

orig_state	dest_state	netmigration
1		1		0	
2		1		25
3		1		.
1		2		-25
2		2		0
3		2		44
1		3		.
2		3		-44
3		3		0


There is an origin state, a destination state, and net migration between the two. I don't want to double count net migration so I only want to keep a single observation for each state pair. Does anyone have any suggestions about how I could get rid of the second observation that gives me the negative net migration of the first observation?


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