The "assign" attribute on model matrices describes which columns
come from which terms in the model formula. It has two versions. R uses
the original version, but the alternate version found in
S-plus is sometimes useful.
Usage
## Default S3 method:
attrassign(object, tt,...)
## S3 method for class 'lm'
attrassign(object,...)
Arguments
object
model matrix or linear model object
tt
terms object
...
ignored
Details
For instance consider the following
survreg(Surv(time, status) ~ age + sex + factor(ph.ecog), lung)
R gives the compact for for assign, a vector (0, 1, 2, 3, 3, 3);
which can be
read as “the first column of the X matrix (intercept) goes with none
of the terms, the second column of X goes with term 1 of the model
equation, the third column of X with term 2, and columns 4-6 with
term 3”.
A list with names corresponding to the term names and elements
that are vectors indicating which columns come from which terms
See Also
terms,model.matrix
Examples
formula <- Surv(time,status)~factor(ph.ecog)
tt <- terms(formula)
mf <- model.frame(tt,data=lung)
mm <- model.matrix(tt,mf)
## a few rows of data
mm[1:3,]
## old-style assign attribute
attr(mm,"assign")
## alternate style assign attribute
attrassign(mm,tt)