Date:         Thu, 18 Nov 2004 04:13:10 -0800
Reply-To:     Dennis Diskin <diskin@SNET.NET>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Dennis Diskin <diskin@SNET.NET>
Subject:      Re: lag1() question
Comments: To: Jason Zhang <qiyuzhang2@YAHOO.COM>
In-Reply-To:  <20041118044125.79499.qmail@web60602.mail.yahoo.com>
Content-Type: text/plain; charset=us-ascii

Jason,

As John Kirpatrick pointed out, LAG(t) returns the value of T at the last call to the lag function. In your example, the first time LAG is called is on the second pass thru the datastep. LAG(T) at that point is missing.

I generally try to avoid LAG entirely unless it is a very simple case.

You could easilly do:

t = .8 ** (_n_ - 1);

HTH,
Dennis Diskin

Jason Zhang <qiyuzhang2@YAHOO.COM> wrote:
Hi,

I want to generate a value for a variable, say t. But
tĄ¯s value depends on previous observationĄ¯s t value.
I used the code:
T=lag1(t)*0.8;

It doesnĄ¯t work. The following is an example of what
I want to do:
data one;
input x;
cards;
1
2
3
4
5
6
;
run;

data two;
set one;
if _n_=1 then t=1; else
t=lag1(t)*0.8;
run;

what I expected for tĄ¯s values are:
1
0.8
0.64
Ą&shy;

Can anyone help me with this? Thanks a lot!!!
Jason





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