Date:         Mon, 7 Nov 2011 14:14:35 -0800
Reply-To:     "Schwarz, Barry A" <barry.a.schwarz@BOEING.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Schwarz, Barry A" <barry.a.schwarz@BOEING.COM>
Subject:      Re: Data step question: why different results
In-Reply-To:  <FA0550A1D186FF49BB0748CD711B17EDD91034B71E@SDPSMSX.QUALNET.ORG>
Content-Type: text/plain; charset="us-ascii"

If the data step contains a set statement, it will always iterate after reaching the last statement.

In scenario 1, the sequence is
   read observation 1 from have1 (x and y get set)
   output observation 1 to want (z missing as expected)
   assign new value to x and z
   output observation 2 to want (y unchanged as expected)
   iterate data step
   attempt to read observation 2 from have1 (no such observation)
   terminate data step

In scenario 2, the sequence is
   assign values to x and z
   output observation 1 to want (y missing as expected)
   read observation 1 from have1 (x and y get set)
   output observation 2 to want (new values for x and y as expected)
   iterate
   assign values to x and z (note that z is reset, not retained)
   output observation 3 to want (y is retained)
   attempt to read observation 2 from have1 (no such observation)
   terminate data step

Since you presented a "solution" without describing the requirement, you are not likely to get any suggestions regarding a general solution.

> -----Original Message-----
> From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of Bian,
> Haikuo
> Sent: Monday, November 07, 2011 12:25 PM
> To: SAS-L@LISTSERV.UGA.EDU
> Subject: Data step question: why different results
>
> Dear list,
>
> Question emerged when I tried to insert rows into SAS table using
> datastep.
>
> /*original table*/
> data have1;
>   x=1;
>   y=2;
> run;
>
> /*Scenario 1*/
> data want;
> set have1;
> output;
> x=23;
> z=34;
> output;
> run;
>
> proc print;run;
> and I got the following:
>
>
>                                       Obs     x    y     z
>
>                                        1      1    2     .
>                                        2     23    2    34
>
> This is understandable to me.
>
> Then I switched the order like this:
>
>  /*Scenario 2*/
> data want;
> x=23;
> z=34;
> output;
> set have1;
> output;
> run;
>
> proc print;run;
>
> Then I got:
>
>                                       Obs     x     z    y
>
>                                        1     23    34    .
>                                        2      1    34    2
>                                        3     23    34    2
>
>
> Question 1: Why the third record? Is it because Datastep will loop again
> after reaching the end? See next scenario.
>                  2. Why value of variable z is automatically retained even
> z is not from a dataset?
>
>
> I can get what I expected by doing:
> /*Scenario 3*/
>
> data want;
> if _n_=1 then do;
> x=23;
> z=34;
> output;
> end;
> set have1;
> output;
> run;
>
> proc print;run;
>
> then I can get:
>
>                                       Obs     x     z    y
>
>                                        1     23    34    .
>                                        2      1    34    2
>
>
>
> Thank you all in advance!
>
> Haikuo
>
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