SPSS® 12.0 Command Syntax Reference

Transformation Expressions 49
• Logical expressions can be simple logical variables or relations, or they can be complex
logical tests involving variables, constants, functions, relational operators, logical
operators, and parentheses to control the order of evaluation.
• On an IF command, a logical expression that is true causes the assignment expression to
be executed. A logical expression that returns missing has the same effect as one that is
false: the assignment expression is not executed and the value of the target variable is not
altered.
• On a DO IF command, a logical expression that is true causes SPSS to execute the
commands immediately following the DO IF, up to the next ELSE IF, ELSE, or END IF. If
it is false, SPSS looks for the next ELSE IF or ELSE command. If the logical expression
returns missing for each of these, the entire structure is skipped.
• On a SELECT IF command, a logical expression that is true causes the case to be selected.
A logical expression that returns missing has the same effect as one that is false: the case
is not selected.
• On a LOOP IF command, a logical expression that is true causes looping to begin (or
continue). A logical expression that returns missing has the same effect as one that is
false: the structure is skipped.
• On an END LOOP IF command, a logical expression that is false returns control to the
LOOP command for that structure and looping continues. If it is true, looping stops and
the structure is terminated. A logical expression that returns a missing value has the same
effect as one that is true: the structure is terminated.
String Variables in Logical Expressions
String variables, like numeric variables, can be tested in logical expressions.
• String variables must be declared before they can be used in a string expression.
• String variables cannot be compared to numeric variables.
• If strings of different lengths are compared, the shorter string is right-padded with blanks
to equal the length of the longer.
• The magnitude of strings can be compared using LT, GT, and so on, but the outcome
depends on the sorting sequence of the computer. Use with caution.
Logical Functions
• Each argument to a logical function (expression, variable name, or constant) must be
separated by a comma.
• The target variable for a logical function must be numeric.
• The functions RANGE and ANY can be useful shortcuts to more complicated specifications
on the IF, DO IF, and other conditional commands. For example, the command
SELECT IF ANY(REGION,’NW’,’NE’,’SE’).
is equivalent to
SELECT IF (REGION EQ ’NW’ OR REGION EQ ’NE’ OR REGION EQ
’SE’).