[R] formula, how to express for transforming the whole model.matrix, data=Orthodont
Peng
l12345p2000 at yahoo.com
Sat Mar 15 15:22:16 CET 2003
Hi, R or S+ users,
I want to make a simple transformation for the model,
but for the whole design matrix.
The model is distance ~ age * Sex, where Sex is a
factor. So the design matrix may look like the
following:
(Intercept) age SexFemale age:SexFemale
1 1 8 0 0
2 1 10 0 0
3 1 12 0 0
4 1 14 0 0
5 1 8 0 0
6 1 10 0 0
7 1 12 0 0
8 1 14 0 0
...
101 1 8 1 8
102 1 10 1 10
103 1 12 1 12
104 1 14 1 14
105 1 8 1 8
106 1 10 1 10
107 1 12 1 12
108 1 14 1 14
I want to have the whole design matrix transformed by
a vector of multiplicator, say c(m1, m2, m3, ... ,
m26, m27 ), for each Subject. Then the design matrix
will look like this.
(Intercept) age SexFemale age:SexFemale
1 m1 8m1 0 0
2 m1 10m1 0 0
3 m1 12m1 0 0
4 m1 14m1 0 0
5 m2 8m2 0 0
6 m2 10m2 0 0
7 m2 12m2 0 0
8 m2 14m2 0 0
...
101 m26 8m26 m26 8m26
102 m26 10m26 m26 10m26
103 m26 12m26 m26 12m26
104 m26 14m26 m26 14m26
105 m27 8m27 m27 8m27
106 m27 10m27 m27 10m27
107 m27 12m27 m27 12m27
108 m27 14m27 m27 14m27
I tried to add a new column in the data, say "m". But
the following formula expression does not work. Since
Sex is a factor.
y ~ m + I(m*age) + I(m*Sex) + I(m*age*Sex)
Moreover, in order to implement the EM from "Robust
Estimation in Linear Mixed-Effects Models
Using the Multivariate t-Distribution" by Dr.
Pinheiro, I also need to transform the response, y, in
the same way.
I did it by writing SAS liked codes (making a new
table, coding factors, finishing transformation,
making groupedData, call lme), but that is not
readable, and it will be complicated to realized that
for any other datasets.
I am wondering whether the formula has some sorts of
expression to realize transformation for the whole
design matrix, especially when having factors in the
formula.
Thanks a lot!
Peng
Peng Liu
------------------------------
Peng Liu |
Division of Statistics |
Northern Illinois University |
De Kalb, IL 60115, USA |
E-mail: pliu at math.niu.edu |
------------------------------
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