dummy Macro to create dummy variables dummy

Visualizing Categorical Data: dummy

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

The dummy macro ( [download] get dummy.sas)

Macro to create dummy variables

Given a character or discrete numerical variable, the DUMMY 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)

Usage

The DUMMY macro takes the following named parameters. The arguments may be listed within parentheses in any order, separated by commas. For example: 

  %dummy(var=sex group,prefix=);

Parameters

DATA=
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(s) can be character or numeric.
PREFIX=
Prefix(s) used to create the names of dummy variables. The default is 'D_'.
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 variable. Otherwise, you can specify BASE=value to make a different value the baseline group.
FULLRANK=
0/1, where 1 indicates that the indicator for the BASE category is eliminated.

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

interact Create interaction variables
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