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Date:         Tue, 23 Sep 2003 16:21:04 -0400
Reply-To:     Venky Chakravarthy <venky.chakravarthy@PFIZER.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Venky Chakravarthy <venky.chakravarthy@PFIZER.COM>
Subject:      Re: FIRST. and LAST. processing and the WHERE statement
Comments: To: Greg Woolridge <greg.woolridge@TAP.COM>

On Mon, 22 Sep 2003 14:52:25 -0500, Greg Woolridge <greg.woolridge@TAP.COM> wrote:

>From what I can see in the SAS documentation, when a BY statement is used >the special variables FIRST. and LAST. are set when an observation is read >into the PDV. The WHERE statement affects whether or not an observation is >read into the PDV. Based on this I think that the WHERE statement could >affect which observation from an input data set is designated as FIRST. >For instance, if a BY group has 5 observations in the input data set, but >the first 2 do not meet the WHERE clause condition (i.e. they are not read >into the PDV) then the third observation would be designated as FIRST. Am >I correct in my assumptions, or am I missing something? > >Greg M. Woolridge >Manager, Study Programming >TAP Pharmaceutical Products Inc. >e-mail: greg.woolridge@tap.com >phone: 847-582-2332 >fax: 847-582-2403

A while ago, when I was testing something with the debugger on, I noticed that the first.var and the last.var are set to 1 before a single observation is even read in. Most likely this is a compile time activity. You can see this by writing out the two variables to the log before the first observation is read. I have deliberately output a data set with 0 observations.

47 data q ; 48 x = 1 ; 49 stop ; 50 run ;

NOTE: The data set WORK.Q has 0 observations and 1 variables. NOTE: DATA statement used: real time 0.01 seconds cpu time 0.00 seconds

51 52 data w ; 53 put first.x= last.x= ; 54 set q ; 55 by x ; 56 run ;

first.x=1 last.x=1

Kind Regards,

Venky


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