Date:         Wed, 4 Jan 2006 00:14:30 -0800
Reply-To:     ljmpll@SOHU.COM
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         ljmpll@SOHU.COM
Organization: http://groups.google.com
Subject:      get the former period value
Comments: To: sas-l@uga.edu
Content-Type: text/plain; charset="iso-8859-1"

In SAS, we can get a lag period value of variant X by the function
lag(X).
   Such as:

X        Lag period value

20
44      20
23      44
18      23
13      18
12      13
63      12
13      63
11      13
18      11
13      18

But How can we get the former period value of variant X?
(i,e. I want to get the follwing result)

X        the former period value

        20
20      44
44      23
23      18
18      13
13      12
12      63
63      13
13      11
11      18
18      13

What programs should I write?
Thanks !