[R] Basic Dummy Variable Creation

kjetil brinchmann halvorsen kjetil at entelnet.bo
Fri Sep 5 18:54:21 CEST 2003

On 5 Sep 2003 at 8:31, Francisco J. Bido wrote:

Yes, model matrix is the answer, and if it has many arguments, it 
also has many reasonable defaults.  When I am trying out a new 
function, I just accept the dafaults for a starter.

> x <- c(1:10)      #data to be broken up into dummy variables
> v <- c(3,5,7)     #breakpoints
> p =  1                #drop this column to avoid dummy variable trap

What about 
f <- cut(x, breaks=c(0,3,5,7,10)
y <- model.matrix( ~ f)

(model matrix will drop the first column for you), and make a column 
for the intercept)
If you want all the columns, and no intercept, replace with

y <- model.matrix( ~ y - 1)
or even 
y <- model.matrix( ~y + 0)

Kjetil Halvorsen

> How can I get a matrix "y" that has the associated dummy variables for 
> columns?	
> Thank You,
> -Francisco
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