Variables that are read by the SET, MERGE, and UPDATE statements are automatically retained between iterations of the data step. Variables that are created in the data set are not automatically retained and need the RETAIN statement if that behavior is desired.

The sample code provided shows the difference in retention between variables that are read from a data set and variables that are created within the data step. When the Program Data Vector (PDV) is created at compile time, variables that are read from a data set are marked for retention. That action holds true even if that variable is not read for a particular observation. Variables that are read from a data set are initialized to missing upon change of a by-group. Variables that are created within the data step are initialized to missing at the start of each iteration of the data step.

For more information, please see the section titled Data Step Processing in the SAS Language Reference: Concepts documentation.

Operating System and Release Information

Product Family	Product	System	SAS Release
			Reported	Fixed*
SAS System	Base SAS	Aster Data nCluster on Linux x64
		DB2 Universal Database on AIX
		DB2 Universal Database on Linux x64
		Greenplum on Linux x64
		Netezza TwinFin 32bit blade
		Netezza TwinFin 32-bit SMP Hosts
		Netezza TwinFin 64-bit S-Blades
		Netezza TwinFin 64-bit SMP Hosts
		Teradata on Linux
		z/OS
		Z64
		OpenVMS VAX
		Microsoft® Windows® for 64-Bit Itanium-based Systems
		Microsoft Windows Server 2003 Datacenter 64-bit Edition
		Microsoft Windows Server 2003 Enterprise 64-bit Edition
		Microsoft Windows XP 64-bit Edition
		Microsoft® Windows® for x64
		OS/2
		Microsoft Windows 8 Pro
		Microsoft Windows 95/98
		Microsoft Windows 2000 Advanced Server
		Microsoft Windows 2000 Datacenter Server
		Microsoft Windows 2000 Server
		Microsoft Windows 2000 Professional
		Microsoft Windows NT Workstation
		Microsoft Windows Server 2003 Datacenter Edition
		Microsoft Windows Server 2003 Enterprise Edition
		Microsoft Windows Server 2003 Standard Edition
		Microsoft Windows Server 2003 for x64
		Microsoft Windows Server 2008
		Microsoft Windows Server 2008 for x64
		Microsoft Windows Server 2012
		Microsoft Windows XP Professional
		Windows 7 Enterprise 32 bit
		Windows 7 Enterprise x64
		Windows 7 Home Premium 32 bit
		Windows 7 Home Premium x64
		Windows 7 Professional 32 bit
		Windows 7 Professional x64
		Windows 7 Ultimate 32 bit
		Windows 7 Ultimate x64
		Windows Millennium Edition (Me)
		Windows Vista
		Windows Vista for x64
		64-bit Enabled AIX
		64-bit Enabled HP-UX
		64-bit Enabled Solaris
		ABI+ for Intel Architecture
		AIX
		HP-UX
		HP-UX IPF
		IRIX
		Linux
		Linux for x64
		Linux on Itanium
		OpenVMS Alpha
		OpenVMS on HP Integrity
		Solaris
		Solaris for x64
		Tru64 UNIX

* For software releases that are not yet generally available, the Fixed Release is the software release in which the problem is planned to be fixed.

This sample demonstrates the difference in behavior between the variable level that is read from a data set, and the variable grade that is created within the data step.

---

/*Create a data set with name and score for each test.*/
data scores;
  input name :$6. test score;
datalines;
Alice 1 84
Alice 2 93
Alice 3 100
Alice 4 65
;

/*Create a data set with the assigned level for name.*/
data levels;
  input name :$6. level :$10.;
datalines;
Alice new
;

/* Merge the scores and levels to create new level values based on test score.              */

/* Since the variable level is marked as being read from a data set, its value is           */
/* retained throughout the by-group.  After the third iteration of the Data step, level is  */ 
/* set to "scholar" based on the IF statement.  Since the variable level is retained, at    */
/* the start of the fourth iteration, the value is still "scholar".  Since the criteria for */ 
/* the IF statement is not met, there is no change made to the variable and it remains      */
/* "scholar".                                                                               */

/* Contrast this with the variable grade which is created in the Data step  It is           */
/* initialized to missing at the beginning of each iteration of the Data step. Thus, at the */
/* start of the fourth iteration, grade has been set to missing and since the criteria for  */
/* the IF statement is not met, there is no new assignment made to the variable grade and   */
/* it remains missing.                                                                      */

data results;
  merge scores levels;
  by name;
  if score > 92 then do;
   level = 'scholar';
   grade = 'A';
  end;
run;

proc print; 
run;

 

                        Obs    name     test    score    level      grade

                         1     Alice      1       84     new
                         2     Alice      2       93     scholar      A
                         3     Alice      3      100     scholar      A
                         4     Alice      4       65     scholar

 

Type:	Usage Note
Priority:
Topic:	Common Programming Tasks ==> Combining Data

Date Modified:	2012-11-15 16:00:38
Date Created:	2012-10-13 14:43:12