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SAS Programming: Working With Variables. Data Step Manipulations. New variables should be created during a Data step Existing variables should be manipulated during a data step. Missing Values in SAS. SAS uses a period (.) to represent missing values in a SAS data set

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data step manipulations
Data Step Manipulations
  • New variables should be created during a Data step
  • Existing variables should be manipulated during a data step
missing values in sas
Missing Values in SAS
  • SAS uses a period (.) to represent missing values in a SAS data set
  • Different SAS procedures and functions treat missing values differently - always be careful when your SAS data set contains missing values
working with numeric variables
Working With Numeric Variables
  • SAS uses the standard arithmetic operators

+, -, *, /, ** (exponentiation)

Note on Missing Values: Arithmetic operators propagate missing values.

  • SAS has many built-in numeric functions

round(variable,value): Rounds variable to nearest unit given by value.

sum(variable1, variable2, …): Adds any number of variables and ignores missing values

acting on selected observations
Acting on Selected Observations
  • Working with selected observations - subsets of a SAS data set - is easy in SAS
  • First, you must decide on a selection process. What is the distinguishing characteristic of the observations you want to work with?
selecting observations if then statements
Selecting Observations: IF-THEN Statements
  • The IF-THEN statement is the most common way to select observations. Format:

IFconditionTHENaction;

  • condition is one or more comparisons. For any observation, condition is either true or false. If condition is true, SAS performs the action.
if then statement example
IF-THEN Statement: Example
  • Suppose INC is a variable representing annual household income and you want to create a dummy variable, DUM, based on income that takes value 1 when income is less than $10,000.

IF INC<10000 THEN DUM=1;

IF INC >=10000 THEN DUM=0;

using obs in condition
Using OBS in condition
  • In a SAS data set, each record has an observation number which is the number stored in the variable OBS
  • OBS can be used in a condition, but you must refer to the observation number using the variable _n_
  • Example: set the first 10 observations of INC equal to zero

IF _n_ <= 10 THEN INC=0;

comparison operators
Comparison Operators
  • There are 6 comparison operators
  • Can use either the symbol or mnemonic

Symbol Mnemonic Meaning

= EQ Equal to

^= NE Not equal to

> GT Greater than

< LT Less than

>= GE Greater than or equal to

<= LE Less than or equal to

multiple comparisons
Multiple Comparisons
  • Can make more than one comparison in condition by using AND/OR
  • AND / &: All parts must be true for condition to be true
  • Or / |: At least one part must be true for condition to be true
  • Be careful when using AND/OR
  • Can use parentheses in condition
selecting observations for new sas data sets
Selecting Observations for New SAS Data Sets
  • Can use IF-THEN statements to create new SAS data sets
  • Either delete or keep selected observations based on condition
deleting observations
Deleting Observations
  • Format for IF-THEN:

IFconditionTHEN DELETE;

  • Example: Removing missing observations. Suppose the variable INC is missing for some households and you want to drop these observations

IFINC=.THEN DELETE;

keeping selected observations
Keeping Selected Observations
  • A more straightforward way to create new SAS data sets is to keep only those observations that meet some condition. Format:

IFcondition;

example
Example
  • The file salary.dat contains data for 93 employees of a Chicago bank. The file contains the following variables:

Y: Salary

X: Years of education

E: Months of previous work experience

T: Number of months after 1/1/69 that the individual was hired

  • First 61 observations are females, last 32 males
example create dummy for males
Example: Create Dummy for Males

*Program to create dummy variables and;

*new SAS data sets ;

data salary;

infile ‘s:\mysas\salary.dat;

input y x e t;

IF _n_ >61 THEN G=1;

IF _n_ <= 60 THEN G=0;

run;

example create data set for males
Example: Create Data Set for Males

*Make a new SAS data set composed of only;

*records for males ;

data males; *New SAS data set;

set=salary; *Created from salary;

IF G=1;

run;

example create data set for females
Example: Create Data Set for Females

*Make a new SAS data set composed of only;

*records for females ;

data females; *New SAS data set;

set=salary; *Created from salary;

IF G=0;

run;

describing data sample statistics
Describing Data: Sample Statistics
  • Format:

PROC UNIVARIATE <option-list>;

VAR variable-list;

BY variable-list;

FREQ variable;

WEIGHT variable;

selected options
Selected Options

DATA=SAS-data-set; Specify Data Set

If omitted, uses most recent

SAS data set

FREQGenerate Frequency Table

NOPRINTSuppress Printed Output

var statement
VAR Statement
  • List of variables to calculate sample statistics for.
  • If no variables are specified, sample statistics are generated for all numeric variables
weight statement
WEIGHT Statement
  • Specifies a numeric variable in the SAS data set whose values are used to weight each observation
by statement
BY Statement
  • Can be used to obtain separate analyses on observations in groups defined by some value of a variable.
  • Example: Suppose SEX=1 if individual is male, SEX=0 if individual is female; EARN=annual earnings.

PROC UNIVARIATE; *Generates statistics;

VAR EARN; *on earnings for men;

BY SEX; *and women;

RUN;

by statements and sorting
BY Statements and Sorting
  • Before using a BY statement, the SAS data set must be sorted on the variable specified
  • SAS puts the observations in order, based on the values of the variables specified in the BY statement.
  • Use PROC SORT
proc sort
PROC SORT
  • FORMAT:

PROC SORT <options>;

BY <options>variables;

  • Sort Order: ascending. For descending, put DESCENDING on BY line
describing data frequencies
Describing Data: Frequencies
  • FORMAT:

PROC FREQ <options>;

BY variables;

TABLES requests</options>;

WEIGHT variable;

one way frequency table
One-Way Frequency Table
  • SEX=1 (Male) SEX=0(Female)
  • EDUCATION=1(Less than High School), =2(High School),=3(Some College),=4(College grad.)
  • EARN=Annual Earnings

PROC FREQ;

TABLES EDUCATION;

RUN;

PROC FREQ;

TABLES EDUCATION;

BY SEX;

RUN;