Keep only duplicate cases

*(Q) I wonder if there is a way that I can capture those patients with all
	their records (for instance, counter=1,2,and 3 for the same person) and
	delete others who appeared only once and who were real unduplicated cases.

*(A) Posted to SPSSX-L list on 2001/09/21 by rlevesque@videotron.ca.

DATA LIST LIST /ss counter.
BEGIN DATA
1 1
1 2
2 1
3 1
3 2
3 3
4 1
5 1
END DATA.
LIST.

* Objective is to delete ss 2, 4 and 5 because these are true unduplicate records.

MATCH FILES FILE=* /BY=ss /FIRST=first /LAST=last.
* If first=last than that record is both the first and the last (it is UNIQUE).
EXECUTE.
SELECT IF last<>first.