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Chapter 4 Creating New Variables Using SAS Functions

Chapter 4 Creating New Variables Using SAS Functions -...

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STAT1303 Data Management 4. Creating New Variables Using SAS Functions 4 Creating New Variables Using SAS Functions In previous chapter, we have used the SAS procedures for data summarization in which simple calculation is performed. In this chapter, the creation of new variables using the SAS functions are discussed because more complicated calculation is necessary for realistic data management and analysis. 4.1 Assignment Statement To create or modify SAS variables, an assignment statement is used in Data Step. Typically, an assignment statement is specified in the form of variable = expression ; The variable receives the new information and the required information / calculations are specified in the expression. When the expression contains character data, we must enclose the data in quotation marks or double quotation marks. To define the required storage for variables (in particular for character variables), the LENGTH statement should be used. Example 4.1. Assignment statement. * Example 4.1 - assignment statement; libname mylib ’D:/temp’; data trade; set mylib.trade1; total = import+retained+reexport; run; proc print; run; Obs year category import retained reexport total 1 1995 1 61158 42953 19534 123645 2 1995 2 562415 142897 546247 1251559 3 1995 3 543075 225708 336550 1105333 ... TOTAL = IMPORT + RETAINED + REEXPORT; Then, a new variable TOTAL which is the sum of IMPORT, RETAINED and REEXPORT, is created. 4.2 Numeric Assignment Operators and Functions 4.2.1 Numeric Variables A numeric variable is a variable whose values are numbers. In SAS, numeric variables are stored and calculated in double-precision floating point representation. All kinds of mathematical operations on numeric variables can be performed by SAS and SAS functions extend the mathematical calculation capability for numeric expressions. HKU STAT1303 (2011-12, Semester 1) 1
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STAT1303 Data Management 4. Creating New Variables Using SAS Functions 4.2.2 Arithmetic Operators Operation Symbol Example Addition + x = y + z Subtraction - x = y - z Multiplication x = y * z Division / x = y / z Exponentiation ⇤⇤ x = y ** z The order of operations in arithmetic expressions follows rules in mathematical expression Parentheses > exponentiation > multiplication and division > addition and subtraction. Example 4.2. Arithmetic operators. * Example 4.2 - Arithematic operators; libname mylib ’D:/temp’; data trade; set mylib.trade1; total = import+retained+reexport; total2 = total**2; run; proc print; run; Obs year category import retained reexport total total2 1 1995 1 61158 42953 19534 123645 15288086025 2 1995 2 562415 142897 546247 1251559 1.5663999E12 3 1995 3 543075 225708 336550 1105333 1.221761E12 ... 4.2.3 Missing Values in Numeric Variables By default, the missing value in data lines (raw data) are represented by a period ( . ). In an expression, a missing numeric value is represented by a period, e.g. export = .; means that a numeric variable EXPORT is created and initialized with missing value. In the output of PROC, a missing numeric value is printed as a period (by default). For some SAS PROCs, missing numeric value is removed from analysis while some of them do not. Indeed, some of them may have options to choose from.
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