SAS 9.4 Language Reference, 6th Edition

about using the SELECT statement conditionally, see “SELECT Statement” in SAS

DATA Step Statements: Reference.

Error Checking When Using Indexes to Randomly

Access or Update Data

The Importance of Error Checking

When reading observations with the SET statement and KEY= option or with the

MODIFY statement, error checking is imperative for several reasons. The most

important reason is that these tools use nonsequential access methods. Therefore, there is

no guarantee that an observation will be located that satisfies the request. Error checking

enables you to direct execution to specific code paths, depending on the outcome of the

I/O operation. Your program continues execution for expected conditions and terminate

execution when unexpected results occur.

Error-Checking Tools

Two tools have been created to make error checking easier when you use the MODIFY

statement or the SET statement with the KEY= option to process SAS data sets:

• _IORC_ automatic variable

• SYSRC autocall macro

_IORC_ is created automatically when you use the MODIFY statement or the SET

statement with KEY=. The value of _IORC_ is a numeric return code that indicates the

status of the I/O operation from the most recently executed MODIFY or SET statement

with KEY=. Checking the value of this variable enables you to detect abnormal I/O

conditions and to direct execution down specific code paths instead of having the

application terminate abnormally. For example, if the KEY= variable value does match

between two observations, you might want to combine them and output an observation.

If they do not match, however, you might want to only write a note to the log.

Because the values of the _IORC_ automatic variable are internal and subject to change,

the SYSRC macro was created to enable you to test for specific I/O conditions while

protecting your code from future changes in _IORC_ values. When you use SYSRC, you

can check the value of _IORC_ by specifying one of the mnemonics listed in the

following table.

Table 23.4 Most Common Mnemonic Values of _IORC_ for DATA Step Processing

Mnemonic Value Meaning of Return Code When Return Code Occurs

_DSENMR The Transaction data set

observation does not exist in the

Master data set.

MODIFY with BY is used and no

match occurs.

518 Chapter 23 • Reading, Combining, and Modifying SAS Data Sets

Mnemonic Value Meaning of Return Code When Return Code Occurs

_DSEMTR Multiple Transaction data set

observations with the same BY

variable value do not exist in the

Master data set.

MODIFY with BY is used and

consecutive observations with the

same BY values do not find a

match in the first data set. In this

situation, the first observation that

fails to find a match returns

_DSENMR. The subsequent

observations return _DSEMTR.

_DSENOM No matching observation was

found in the Master data set.

SET or MODIFY with KEY=

finds no match.

_SENOCHN The output operation was

unsuccessful.

the KEY= option in a MODIFY

statement contains duplicate

values.

_SOK The I/O operation was successful. a match is found.

Example 1: Routing Execution When an Unexpected Condition

Occurs

Overview

This example shows how to prevent an unexpected condition from terminating the

DATA step. The goal is to update a master data set with new information from a

transaction data set. This application assumes that there are no duplicate values for the

common variable in either data set.

Note: This program works as expected only if the master and transaction data sets

contain no consecutive observations with the same value for the common variable.

For an explanation of the behavior of MODIFY with KEY= when duplicates exist,

see the MODIFY statement in SAS DATA Step Statements: Reference.

Input Data Sets

The Transaction data set contains three observations: two updates to information in

Master and a new observation about PartNumber value 6 that needs to be added. Master

is indexed on PartNumber. There are no duplicate values of PartNumber in Master or

Transaction. The following shows the Master and the Transaction input data sets:

Master Transaction

OBS PartNumber Quantity OBS PartNumber AddQuantity

1 1 10 1 4 14

2 2 20 2 6 16

3 3 30 3 2 12

4 4 40

5 5 50

Error Checking When Using Indexes to Randomly Access or Update Data 519