Date:         Wed, 29 Mar 2000 05:19:47 GMT
Reply-To:     N Yiannakoulias <nwy@GPU.SRV.UALBERTA.CA>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         N Yiannakoulias <nwy@GPU.SRV.UALBERTA.CA>
Organization: University of Alberta
Subject:      selecting controls...help?

Hi all,

Yet another programming task that has me stumped:
I have two files -a case file and a control pool:

Case file                       Control file
ID1     DATE1           ID2     DATE2   DATE3
1       1997            1       1994    1995
2       1993            2       1998    1997
3       1995            3       1997    1999
4       1997            4       1999    1999
5       1998            5       1999    1999
6       1993            6       1999    1998
...                     7       1998    1999
n=2500                  8       1998    1997
                        ...
                        n=80 000 (randomly ordered)

I need to match 4 controls to each case.  A control
is matched to a case if DATE2 and DATE3 are >
DATE1.  Once a control is successfully matched
to a case, it is removed from the pool.  The resultant
Control file should look like this:

Control file
ID2     DATE2   DATE3   MATCH
1       1994    1995    2
2       1998    1997    2
3       1997    1999    2
4       1999    1999    1
5       1999    1999    1
6       1999    1998    1
7       1998    1999    1
8       1998    1997    2
...
n=10 000 (4 controls for each case)

Any suggestions/hints would greatly appreciated,

N