From: Mark Difford <mark_difford_at_yahoo.co.uk>

Date: Wed, 12 Dec 2007 02:10:31 -0800 (PST)

Date: Wed, 12 Dec 2007 02:10:31 -0800 (PST)

Whoops! Sorry, forgot my session stuff, just in case ...

R version 2.6.1 RC (2007-11-22 r43520)

i386-pc-mingw32

locale:

LC_COLLATE=English_South Africa.1252;LC_CTYPE=English_South
Africa.1252;LC_MONETARY=English_South

Africa.1252;LC_NUMERIC=C;LC_TIME=English_South Africa.1252

attached base packages:

[1] tcltk splines stats graphics grDevices utils datasets methods base

other attached packages:

[1] debug_1.1.0 mvbutils_1.1.1 MASS_7.2-38 sfsmisc_1.0-0 ade4_1.4-5
Design_2.1-1

[7] survival_2.34 Hmisc_3.4-3

loaded via a namespace (and not attached):
[1] cluster_1.11.9 gamlss_1.7-0 grid_2.6.1 lattice_0.17-2
latticeExtra_0.3-1

[6] rcompgen_0.1-17 tools_2.6.1

Mark Difford wrote:

*>
*

> Dear List-members,

*>
**> Hopefully someone will help through my confusion:
**>
**> In order to get the same coefficients as we get from the following
**>
**> ##
**> require (MASS)
**> summary ( lm(Gas ~ Insul/Temp - 1, data = whiteside) )
**>
**> ......................
**>
**> we need to do the following (if we use model.matrix to specify the model)
**>
**> ##
**> summary ( lm(Gas ~ model.matrix(~ Insul/Temp - 1) - 1, data = whiteside) )
**>
**> ......................
**>
**> That is, we need to take out "two intercepts." Is this "correct"?
**> Shouldn't lm check to see if an intercept has been requested as part of
**> the model formula?
**>
**> If I do
**> ##
**> summary(lm(as.formula(Gas ~ model.matrix (~ Insul/Temp-1,
**> data=whiteside)), data=whiteside))
**>
**> .......................
**>
**> we get a strange model. But the formula part of this model qualifies as a
**> valid formula
**> ##
**> as.formula(Gas ~ model.matrix (~ Insul/Temp-1, data=whiteside))
**>
**> ----------------
**>
**> just as if I were to write: lm(Gas ~ Insul/Temp - 1, data=whiteside)
**>
**> But we know that the _correct_ formula is the following
**>
**> ##
**> as.formula(Gas ~ model.matrix (~ Insul/Temp-1, data=whiteside) -1)
**>
**> -----------------
**>
**> (Sorry, this is getting really long) --- So, my question/confusion comes
**> down to wanting to know why lm() doesn't check to see if an intercept has
**> been specified when the model has been specified using model.matrix.
**>
**> Regards,
**> Mark.
**>
**>
*

-- View this message in context: http://www.nabble.com/lm-model.matrix-confusion-%28--bug%29-tp14292188p14292212.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Wed 12 Dec 2007 - 10:18:41 GMT

Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.

Archive generated by hypermail 2.2.0, at Wed 12 Dec 2007 - 11:30:18 GMT.

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help.
Please read the posting
guide before posting to the list.
*