dummy Construct dummy variables for a factor dummy

SAS Macro Programs: dummy

$Version: 1.3 (18 Mar 2001)
Michael Friendly
York University

dummy macro ( [download] get dummy.sas)

Given a character or discrete numerical variable, this macro creates dummy (0/1) variables to represent the levels of the original variable in a regression model. If the original variable has c levels, (c-1) new variables are produced (or c variables, if FULLRANK=0)

The dummy variables can be named by appending numbers to a prefix, or by appending the value of the discrete variable to the prefix.

Parameters

DATA=_LAST_
The name of the input dataset. If not specified, the most recently created dataset is used.
OUT=
The name of the output dataset. If not specified, the new variables are appended to the input dataset.
VAR=
The name(s) of the input variable(s) to be dummy coded. Must be specified. The variable can be character or numeric. If several variables are given, specify their names individually (lists such as X1-X5 are not allowed).
PREFIX=
Prefix used to create the names of dummy variabbles. The default is 'D_'. The prefix may be empty.
NAME=
If NAME=VAL, the dummy variables are named by appending the value of the VAR= variable to the prefix. Otherwise, the dummy variables are named by appending numbers, 1, 2, ... to the prefix. The resulting name must be 8 characters or less.
BASE=
Indicates the level of the baseline category, which is given values of 0 on all the dummy variables. BASE=_FIRST_ specifies that the lowest value of the VAR= variable is the baseline group; BASE=_LAST_ specifies the highest value of the vartiable. Otherwise, you can specify BASE=value to make a different value the baseline group.

Example

With the input data set, 
 data test;
   input y group $ @@;
  cards;
  10  A  12  A   13  A   18  B  19  B  16  C  21  C  19  C  
  ;
The macro statement: 
	 %dummy ( data = test, var = group) ;
produces two new variables, D_A and D_B. Group C is the baseline category (corresponding to BASE=_LAST_) 
		OBS     Y    GROUP    D_A    D_B
		
		 1     10      A       1      0
		 2     12      A       1      0
		 3     13      A       1      0
		 4     18      B       0      1
		 5     19      B       0      1
		 6     16      C       0      0
		 7     21      C       0      0
		 8     19      C       0      0

See also