Re: [R] how to use the basis matrix of "ns" in R? really confused by multi-dim spline filtering?

From: Michael <comtech.usa_at_gmail.com>
Date: Tue 28 Feb 2006 - 20:19:55 EST

Thanks a lot! I happened to have read Professor Harrell's book before I post. It did not have any detailed examples/guides about using splines in R, esp. multiple dimensions... I am in need of hands on examples of putting theories into reality in R...

On 2/27/06, Liaw, Andy <andy_liaw@merck.com> wrote:
>
> You want something more useful, here are a couple:
>
> Prof. David Ruppert has some slides from his talks that contain quite
> simple explanations of how regression splines work.
>
> I'll also say one thing that I've said on this list before: Get a copy of
> Prof. Harrell's Regression Modeling Strategies, and read it over and
> over until you can memorize it backward.
>
> Andy
>
> -----Original Message-----
> *From:* Michael [mailto:comtech.usa@gmail.com]
> *Sent:* Monday, February 27, 2006 5:31 PM
> *To:* Liaw, Andy
> *Cc:* vito muggeo; R-help@stat.math.ethz.ch
> *Subject:* Re: [R] how to use the basis matrix of "ns" in R? really
> confused by multi-dim spline filtering?
>
> I think you mis-understood. And perhaps you read in a haste, or you were
> just in a bad mood today.
>
> I think on this mailing-list, many people come for help on a R related
> issue, they know something theoretically, but since they are new to R, they
> want to use R, they want to use R to help do applied things.
>
> For me, there is a missing link between my understanding of splines from
> the books(which are abstract) and a usage example in R. That's something I
> am looking for. I believe it is very appropriate.
>
> If you don't know, or don't want to say anything helpful, please just
> don't say anything. It is not about a gun pointing, it is about a learning
> process which is very specific to R.
>
> Please kindly try not to say negative things, and try to discourage people
> from learning new things.
>
> On 2/27/06, Liaw, Andy < andy_liaw@merck.com> wrote:
>
> > If you do not understand what ns() outputs, nor descriptions of splines
> > in
> > books, perhaps it's not an appropriate tool for you. Look for something
> > that you understand (or can understand after some reading). No one is
> > pointing a gun to your head and tell you to use splines, I hope.
> >
> > If you have a hard time understanding what you read in books, it's
> > unrealistic to expect a mailing list about a software to teach you.
> >
> > Andy
> >
> > From: Michael
> > >
> > > Have you seen an example on how to do it in R? I found no practical
> > > examples...
> > >
> > > On 2/27/06, vito muggeo <vmuggeo@dssm.unipa.it> wrote:
> > > >
> > > > Dear Micheal,
> > > >
> > > > > the output of the "ns" function in R is "basis matrix", but then
> > > > Yes you are right, the output of the ns(x, df) is the basis
> > > matrix of a
> > > > natural cubic spline with df degrees of freedom. See ?ns (in package
> > > > splines) on how to specify df or knots or ..
> > > >
> > > > Fitting y~ns(x,df) yields a smooth curve given by a linear
> > > combination
> > > > of the basis functions (the single colums of the basis
> > > matrix) by the
> > > > estimated coefficients (returned by the fitted model).
> > > >
> > > > As far as I know, a tensor product is usually employed to
> > > > multidimensional smoothing and the multidimensional basis
> > > is formed via
> > > > the kronecker product of the marginal bases.
> > > >
> > > > Finally, last but not least: Probably you need some statistical
> > > > backaground on spline fitting..
> > > > Please, read some statistical papers/books on such topic
> > > (for instance
> > > > see references in packages splines, mgcv)
> > > >
> > > > best,
> > > > vito
> > > >
> > > > Michael wrote:
> > > > > Hi all,
> > > > >
> > > > > Could anybody recommend some easy-to-understand and example based
> > > > > notes/tutorials on how to use cubic splines to do filtering on
> > > > > multi-dimension data?
> > > > >
> > > > > I am confused by the 1-dimensional case, and more confused by
> > > > > multi-dimensional case.
> > > > >
> > > > > I found all the books suddenly become very abstract when
> > > it comes to
> > > > this
> > > > > subject.
> > > > >
> > > > > They don't provide examples in R or Splus at all.
> > > > >
> > > > > Specifically, I don't know how to provide data "x" to the
> > > "ns" function
> > > > in
> > > > > R,
> > > > >
> > > > > and I don't understand what should be the output matrix,
> > > and how to use
> > > > the
> > > > > output matrix to "filter" data?
> > > > >
> > > > > Books mention about basis matrix, design matrix, model
> > > matrix, data
> > > > matrix,
> > > > > etc. I got lost.
> > > > >
> > > > > I presume the output of the "ns" function in R is "basis
> > > matrix", but
> > > > then
> > > > > how do I use it? How to form tensor-product?
> > > > >
> > > > > I don't understand it at all.
> > > > >
> > > > > Please help me!
> > > > >
> > > > > Thank you very much!
> > > > >
> > > > > [[alternative HTML version deleted]]
> > > > >
> > > > > ______________________________________________
> > > > > R-help@stat.math.ethz.ch mailing list
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> > > > > PLEASE do read the posting guide!
> > > > http://www.R-project.org/posting-guide.html
> > > > >
> > > >
> > > > --
> > > > ====================================
> > > > Vito M.R. Muggeo
> > > > Dip.to Sc Statist e Matem `Vianelli'
> > > > UniversitÓ di Palermo
> > > > viale delle Scienze, edificio 13
> > > > 90128 Palermo - ITALY
> > > > tel: 091 6626240
> > > > fax: 091 485726/485612
> > > > ====================================
> > > >
> > >
> > > [[alternative HTML version deleted]]
> > >
> > >
> >
> >
> >
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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Feb 28 20:29:12 2006

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