SPSS® 12.0 Command Syntax Reference

496 DO IF
Example
DATA LIST FREE / X(F1).
NUMERIC #QINIT.
DO IF NOT #QINIT.
+ PRINT EJECT.
+ COMPUTE #QINIT = 1.
END IF.
PRINT / X.
BEGIN DATA
1 2 3 4 5
END DATA.
EXECUTE.
• This example shows how to execute a command only once.
• The NUMERIC command creates scratch variable #QINIT, which is initialized to 0.
• The NOT logical operator on DO IF reverses the outcome of a logical expression. In this
example, the logical expression is a numeric variable that takes only 0 (false) or 1 (true)
as its values. The PRINT EJECT command is executed only once, when the value of
scratch variable #QINIT equals 0. After the COMPUTE command sets #QINIT to 1, the DO
IF structure is skipped for all subsequent cases. A scratch variable is used because it is
initialized to 0 and is not reinitialized after each case.
ELSE Command
ELSE executes one or more transformations when none of the logical expressions on DO IF
or any ELSE IF commands is true.
• Only one ELSE command is allowed within a DO IF—END IF structure.
• ELSE must follow all ELSE IF commands (if any) in the structure.
• If the logical expression on DO IF or any ELSE IF command is true, the program ignores
the commands following ELSE.
Example
DO IF (X EQ 0).
COMPUTE Y=1.
ELSE.
COMPUTE Y=2.
END IF.
• Y is set to 1 for all cases with value 0 for X, and Y is 2 for all cases with any other valid
value for X.
• The value of Y is not changed by this structure if X is missing.