| attrassign {survival} | R Documentation |
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.
## Default S3 method: attrassign(object, tt,...) ## S3 method for class 'lm' attrassign(object,...)
object |
model matrix or linear model object |
tt |
terms object |
... |
ignored |
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”.
The alternate (S-Plus default) form is a list
$(Intercept) 1
$age 2
$sex 3
$factor(ph.ecog) 4 5 6
A list with names corresponding to the term names and elements that are vectors indicating which columns come from which terms
formula <- Surv(time,status)~factor(edema) tt <- terms(formula) mf <- model.frame(tt,data=pbc) 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)