Programming in SAS
How SAS implements
structured programming
constructs
SAS Philosophy
The “Elephant philosophy
of programming”
Remove everything that doesn’t look like
an elephant.
SAS manipulates tables one row at a time.
DATA Steps
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Program statements are executed within data steps
Code is executed in the order that it appears
Instruction sets in SAS end with a DATA, PROC, or RUN
statement
Each DATA step executes an implied loop from the first
read statement (SET, MERGE, INPUT, etc.) to the start of
the next instruction set
Data records are output at the end of the instruction set
(implied OUTPUT) unless there is an OUTPUT statement
Sequence
Statement 1
Statement 2
Statement 3
Statement 4
Statement …
Loops
Setup Statements
DO WHILE
Statement 1
Statement 2
Statement 3
Setup Statements
Statement 1
Statement 2
Statement 3
***
***
Statement n
Statement n
DO UNTIL
DO Statement
DO;
...more SAS statements...
END;
DO index-variable=specification-1 <, . . .
specification-n>;
. . . more SAS statements . . .
END;
DO WHILE|UNTIL Statement
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The UNTIL expression is evaluated at the
bottom of the loop after the statements in the
DO loop have been executed. If the expression
is true, the DO loop does not iterate again.
The WHILE expression is evaluated at the top
of the loop before the statements in the DO
loop are executed. If the expression is true, the
DO loop iterates. If the expression is false the
first time it is evaluated, the DO loop does not
iterate even once.
Examples
n=0;
do while(n<5);
n= n+1;
put n;
end;
n=0;
do until (n<5);
n= n+1;
put n;
end;
Examples
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do i=1 to 10;
do count=2 to 8 by 2;
do i=1 to 10 while (x<y);
do i=2 to 20 by 2 until((x/3)>y);
Selection
Select
Case 1
Case 2
Case 3
Statement 1a Statement 1b Statement 1c
Statement 2a Statement 2b Statement 2c
Statement 3a Statement 3c Statement 3c
Statement … Statement … Statement …
IF-THEN/ELSE Statement
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IF expression THEN statement;
<ELSE statement;>
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Arguments
expression
•
is any SAS expression and is a required argument.
statement
•
can be any executable SAS statement or DO group.
SAS Selection Constructs
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IF … THEN …; ELSE …;
IF … THEN
• DO;
•
•
• END
ELSE
• DO;
•
•
Statements
Statements
• END;
Other else statements.
SELECT Statement
SELECT <(select-expression)>;
WHEN-1 (when-expression-1 <..., whenexpression-n>) statement;
<... WHEN-n (when-expression-1 <..., whenexpression-n>) statement;>
<OTHERWISE statement;
END;
• (select-expression) specifies any SAS
•
expression that evaluates to a single value.
(when-expression) specifies any SAS
expression, including a compound expression.
SAS Selection Constructs
(cont.)
SELECT (payclass);
WHEN ('monthly') amt=salary;
WHEN ('hourly')
DO;
amt=hrlywage*min(hrs,40);
IF hrs>40 THEN PUT 'Check Timecard';
END; /* end of do */
OTHERWISE PUT 'Problem Observation';
END;