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IFN Function介绍
Returns a numeric value based on whether an expression is true, false, or missing.

IFN(logical-expression, value-returned-when-true, value-returned-when-false <,value-returned-when-missing>)


MISSING Function
Returns a numeric result that indicates whether the argument contains a missing value.

Syntax

MISSING(numeric-expression | character-expression)

Arguments
numeric-expression specifies a numeric constant, variable, or expression.
character-expression specifies a character constant, variable, or expression.

CALL MISSING Routine
Assigns missing values to the specified character or numeric variables.

Syntax

CALL MISSING(varname1<, varname2, ...>);

Arguments

varname specifies the name of SAS character or numeric variables.

早上有一个相似的程序。

学习了ifn函数。