例如x为四分类的变量,则需要产生四个哑变量(事实上分析时一般只需要纳入三个哑变量即可,以未纳入的作为reference group)
| X 
 | X1 
 | X2 
 | X3 
 | X4 
 | 
| 1 
 | 1 
 | 0 
 | 0 
 | 0 
 | 
| 2 
 | 0 
 | 1 
 | 0 
 | 0 
 | 
| 3 
 | 0 
 | 0 
 | 1 
 | 0 
 | 
| 4 
 | 0 
 | 0 
 | 0 
 | 1 
 | 
在SAS中实现
先建立数据集a,
data a;
input x@@;
cards;
1 2 3 4
;
run;
 
方法一:
data b;
set a;
x1=(x=1);
x2=(x=2);
x3=(x=3);
x4=(x=4);
run;
 
方法二:
data c;
set a;
array a{4} x1 x2 x3 x4;
do i= 1 to 4;
a{i}=(x=i);
end;
drop i;
run;
 
方法三:
data d;
set a;
if x=1 then x1=1;else x1=0;
if x=2 then x2=1;else x2=0;
if x=3 then x3=1;else x3=0;
if x=4 then x4=1;else x4=0;
run;
 
方法四:
data e;
set a;
array a{4} x1 x2 x3 x4;
do i= 1 to 4;
if x=1 then a{i}=i;else a{i}=0;
end;
drop i;
run;