From: Spencer Graves <spencer.graves at pdf.com>
To: Prof Brian Ripley <ripley at stats.ox.ac.uk>
CC: Oana Mocila <oanaom at hotmail.com>, r-help at stat.math.ethz.ch
Subject: Re: [R] parameterization of factor in R
Date: Tue, 27 Dec 2005 12:27:05 -0800
If you are not familiar with MASS (Modern Applied Statistics with S, 4th
ed, Venables and Ripley 2002, Springer), I can assure you it is an
excellent reference for learning R. There are many books on R that I have
not read, but among the books in my personal library, I refer to MASS
fairly frequently. If it is beyond your budget and not in a local library,
I encourage you to investigate the possibility of having that library
obtain a copy. If the library needs justification, please explain what you
know of the book, how it became recommended for you, the problems you hope
it will help you solve, etc.
Spencer Graves
Prof Brian Ripley wrote:
?contr.sum
And Chapter 6 of MASS would have explained all this to you, so if you have
further questions please consult it.
On Tue, 27 Dec 2005, Oana Mocila wrote:
I encountered this problem with parameterization in R:
I have two factors in a regression. how about if I want to
set constraint so that for each factor, the sum of their
coefficients equals to zero(instead of choosing a reference
category)? for example, I have factor(variable) A(with three
categories) and factor(variable) B(with 4 categories), and I want
to parameterize so that the sum of the three coefficients of
A = 0, and sum of the four coefficients of B = 0? I
mean how to do it in R?
--
Spencer Graves, PhD
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