IF condition variable=expression.
or
IF condition vector(index)=expression.
The IF transformation conditionally assigns the value of a target
expression to a target variable, based on the truth of a test
expression.
Specify a boolean-valued expression (see Mathematical Expressions) to be tested
following the IF keyword. This expression is evaluated for each case.
If the value is true, then the value of the expression is computed and
assigned to the specified variable. If the value is false or missing,
nothing is done. Numeric and string variables may be
assigned. When a string expression’s width differs from the target
variable’s width, the string result of the expression is truncated or
padded with spaces on the right as necessary. The expression and
variable types must match.
The target variable may be specified as an element of a vector (see VECTOR). In this case, a vector index expression must be specified in parentheses following the vector name. The index expression must evaluate to a numeric value that, after rounding down to the nearest integer, is a valid index for the named vector.
Using IF to assign to a variable specified on LEAVE
(see LEAVE) resets the variable’s left state. Therefore,
LEAVE should be specified following IF, not before.
When IF is specified following TEMPORARY
(see TEMPORARY), the LAG function may not be used
(see LAG).