SELECT

SELECT

Executes one of several statements or groups of statements

Valid: in a DATA step

Category: Control

Type: Executable

Syntax
Arguments
Details
Comparisons
Examples
	Example 1: Using Statements
	Example 2: Using DO Groups
	Example 3: Using a Compound Expression
	Example 4: Making Comparisons for Equality
See Also

Syntax

SELECT <(select-expression)>;

WHEN-1 (when-expression-1 <..., when-expression-n>) statement;

<... WHEN-n (when-expression-1 <..., when-expression-n>) statement;>

<OTHERWISE statement;>

END;

Arguments

(select-expression)

specifies any SAS expression that evaluates to a single value.

(when-expression)

specifies any SAS expression, including a compound expression. SELECT requires you to specify at least one when-expression.

Tip:	Separating multiple *when-expressions* with a comma is equivalent to separating them with the logical operator OR.
Tip:	The way a *when-expression* is used depends on whether a *select-expression* is present.
Explanation:	If the *select-expression* is present, SAS evaluates the *select-expression* and *when-expression. SAS compares the two for equality and returns a value of true or false. If the comparison is true, statement* is executed. If the comparison is false, execution proceeds either to the next *when-expression* in the current WHEN statement, or to the next WHEN statement if no more expressions are present. If no WHEN statements remain, execution proceeds to the OTHERWISE statement, if one is present. If the result of all SELECT-WHEN comparisons is false and no OTHERWISE statement is present, SAS issues an error message and stops executing the DATA step. If no *select-expression* is present, the *when-expression* is evaluated to produce a result of true or false. If the result is true, *statement* is executed. If the result is false, SAS proceeds to the next *when-expression* in the current WHEN statement, or to the next WHEN statement if no more expressions are present, or to the OTHERWISE statement if one is present. (That is, SAS performs the action that is indicated in the first true WHEN statement.) If the result of all *when-expressions* is false and no OTHERWISE statement is present, SAS issues an error message. If more than one WHEN statement has a true *when-expression, only the first WHEN statement is used; once a when-expression* is true, no other *when-expressions* are evaluated.

statement

can be any executable SAS statement, including DO, SELECT, and null statements. You must specify the statement argument.

Details

The SELECT statement begins a SELECT group; SELECT groups contain WHEN statements that identify SAS statements that are executed when a particular condition is true. Use at least one WHEN statement in a SELECT group. An optional OTHERWISE statement specifies a statement to be executed if no WHEN condition is met. An END statement ends a SELECT group.

Null statements that are used in WHEN statements cause SAS to recognize a condition as true without taking further action. Null statements that are used in OTHERWISE statements prevent SAS from issuing an error message when all WHEN conditions are false.

Comparisons

When you have a long series of mutually exclusive conditions, using a SELECT group is more efficient than using a series of IF-THEN statements because CPU time is reduced. Large numbers of conditions make a SELECT group more efficient than IF-THEN/ELSE statements because CPU time is reduced. SELECT groups also make the program easier to read and debug.
Use IF-THEN/ELSE statements for programs with few statements. Subsetting IF statements should be used without a THEN clause to continue processing only those observations or records that meet the condition that is specified in the IF clause.

Examples

Example 1: Using Statements

select (a);
   when (1) x=x*10;
   when (2);
   when (3,4,5) x=x*100;
   otherwise;
end;

Example 2: Using DO Groups

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;               /* end of select */

Example 3: Using a Compound Expression

select;
   when (mon in ('JUN', 'JUL', 'AUG') 
   and temp>70) put 'SUMMER ' mon=;
   when (mon in ('MAR', 'APR', 'MAY')) 
   put 'SPRING ' mon=;
   otherwise put 'FALL OR WINTER ' mon=;
end;

Example 4: Making Comparisons for Equality

   /* INCORRECT usage to select value of 2 */
select (x);
   /* evaluates T/F and compares for       */
   /* equality with x                      */
   when (x=2) put 'two';    
end;                        


   /* correct usage */
select(x);
   /* compares 2 to x for equality */
   when (2) put 'two';     
end;


   /* correct usage */
select;
   /* compares 2 to x for equality         */
   when (x=2) put 'two';    
end;

Chapter Contents
Previous
Next
Top of Page

Valid:	in a DATA step
Category:	Control
Type:	Executable