SPSS® 12.0 Command Syntax Reference

494 DO IF
Logical Expressions
• Logical expressions can be simple logical variables or relations, or they can be complex
logical tests involving variables, constants, functions, relational operators, and logical
operators. Logical expressions can use any of the numeric or string functions allowed in
COMPUTE transformations (see COMPUTE).
• Parentheses can be used to enclose the logical expression itself and to specify the order
of operations within a logical expression. Extra blanks or parentheses can be used to make
the expression easier to read.
• Blanks (not commas) are used to separate relational operators from expressions.
• A relation can include variables, constants, or more complicated arithmetic expressions.
Relations cannot be abbreviated. For example, the first relation below is valid; the second
is not:
Valid: (A EQ 2 OR A EQ 5)
Not valid: (A EQ 2 OR 5)
• A relation cannot compare a string variable to a numeric value or variable, or vice versa.
A relation cannot compare the result of a logical function (SYSMIS, MISSING, ANY, or
RANGE) to a number.
Operations
• DO IF marks the beginning of the control structure and END IF marks the end. Control for
a case is passed out of the structure as soon as a logical condition is met on a DO IF, ELSE
IF, or ELSE command.
• A logical expression is evaluated as true, false, or missing. A transformation specified for
a logical expression is executed only if the expression is true.
• Logical expressions are evaluated in the following order: functions, exponentiation, arithmetic
operations, relations, and finally, logical operators. (For strings, the order is functions,
relations, and then logical operators.) When more than one logical operator is used,
NOT is evaluated first, followed by AND and then OR. You can change the order of operations
using parentheses.
• Numeric variables created within a DO IF structure are initially set to the system-missing
value. By default, they are assigned an F8.2 format.
• New string variables created within a DO IF structure are initially set to a blank value and
are assigned the format specified on the STRING command that creates them.
• If the transformed value of a string variable exceeds the variable’s defined format, the
value is truncated. If the value is shorter than the format, the value is right-padded with
blanks.
• If WEIGHT is specified within a DO IF structure, it takes effect unconditionally.
• Commands like SET, DISPLAY, SHOW, and so forth specified within a DO IF structure are
executed when they are encountered in the command file.
• The DO IF—END IF structure (like LOOP—END LOOP) can include commands such as
DATA LIST, END CASE, END FILE, and REREAD, which define complex file structures.