[R] Basic Dummy Variable Creation
Francisco J. Bido
bido at mac.com
Fri Sep 5 15:31:59 CEST 2003
While looking through the mailing list archive, I did not come across a
simple minded example regarding the creation of dummy variables. The
Gauss language provides the command "y = dummydn(x,v,p)" for creating
x = Nx1 vector of data to be broken up into dummy variables.
v = Kx1 vector specifying the K-1 breakpoints
p = positive integer in the range [1,K], specifying which column should
be dropped in the matrix of dummy variables.
y = Nx(K-1) matrix containing the K-1 dummy variables.
My recent mailing list archive inquiry has led me to examine R's
"model.matrix" but it has so many options that I'm not seeing the
forest because of the trees. Is that really the easiest way? or is
there something similar to the dummydn command described above?
To provide a concrete scenario, please consider the following. Using
the above notation, say, I had:
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
How can I get a matrix "y" that has the associated dummy variables for
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