SAS 9.4 Language Reference, 6th Edition

input TeamName $ ParticipantName $ Event1 Event2 Event3;

TeamTotal + (Event1 + Event2 + Event3);

datalines;

Knights Sue 6 8 8

Cardinals Jane 9 7 8

Knights John 7 7 7

Cardinals Lisa 8 9 9

Cardinals Fran 7 6 6

Knights Walter 9 8 10

;

proc print data=total_points;

title 'Total Team Scores';

run;

Output 20.1 Output from the Walk-through DATA Step

About DATA Step Execution

The Default Sequence of Execution in the DATA Step

The following table outlines the default sequence of execution for statements in a DATA

step. The DATA statement begins the step and identifies usually one or more SAS data

sets that the step will create. (You can use the keyword _NULL_ as the data set name if

you do not want to create an output data set.) Optional programming statements process

your data. SAS then performs the default actions at the end of processing an observation.

Table 20.1 Default Execution for Statements in a DATA Step

Structure of a DATA Step Action

DATA statement begins the step

counts iterations

Data-reading statements:

*

About DATA Step Execution 419

Structure of a DATA Step Action

INPUT describes the arrangement of values in the

input data record from a raw data source

SET reads an observation from one or more SAS

data sets

MERGE joins observations from two or more SAS data

sets into a single observation

MODIFY replaces, deletes, or appends observations in

an existing SAS data set in place

UPDATE updates a master file by applying transactions

Optional SAS programming statements, for

example:

further processes the data for the current

observation

FirstQuarter=Jan+Feb+Mar;

if RetailPrice < 500;

computes the value for FirstQuarter for the

current observation

subsets by value of variable RetailPrice for the

current observation

Default actions at the end of processing an

observation

At end of DATA step:

Automatic write, automatic

return

At top of DATA step:

Automatic reset

writes an observation to a SAS data set

returns to the DATA statement

resets values to missing in program data

vector

*

The table shows the default processing of the DATA step. You can alter the sequence of statements in the

DATA step. You can code optional programming statements, such as creating or reinitializing a constant,

before you code a data-reading statement.

Note: You can also use functions to read and process data. For information about how

statements and functions process data differently, see “Using Functions to

Manipulate Files” in SAS Functions and CALL Routines: Reference. For specific

information about SAS functions, see the SAS File I/O and External Files categories

in “SAS Functions and CALL Routines by Category” in SAS Functions and CALL

Routines: Reference.

Changing the Default Sequence of Execution

Using Statements to Change the Default Sequence of Execution

You can change the default sequence of execution to control how your program

executes. SAS language statements offer you a lot of flexibility to do this in a DATA

step. The following list shows the most common ways to control the flow of execution in

a DATA step program.

420 Chapter 20 • DATA Step Processing

Table 20.2 Common Methods That Alter the Sequence of Execution

Task Possible Methods

Read a record merge, modify, join data sets

read multiple records to create a single observation

randomly select records for processing

read from multiple external files

read selected fields from a record by using statement or data

set options

Process data use conditional logic

retain variable values

Write an observation write to a SAS data set or to an external file

control when output is written to a data set

write to multiple files

For more information, see the individual statements in SAS DATA Step Statements:

Reference.

Using Functions to Change the Default Sequence of Execution

You can also use functions to read and process data. For information about how

statements and functions process data differently, see “Using Functions to Manipulate

Files” in SAS Functions and CALL Routines: Reference..

Altering the Flow for a Given Observation

You can use statements, statement options, and data set options to alter how SAS

processes specific observations. The following table lists SAS language elements and

their effects on processing.

Table 20.3 Language Elements That Alter Programming Flow

SAS Language Element Function

subsetting IF statement stops the current iteration when a condition is false,

does not write the current observation to the data

set, and returns control to the top of the DATA step.

IF-THEN/ELSE statement executes a SAS statement for observations that

meet the current condition and continues with the

next statement.

DO loops cause parts of the DATA step to be executed

multiple times.

LINK and RETURN statements alter the flow of control, execute statements

following the label specified, and return control of

the program to the next statement following the

LINK statement.

About DATA Step Execution 421