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

From: Liaw, Andy <andy_liaw_at_merck.com>
Date: Tue 28 Feb 2006 - 08:47:58 EST


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
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > 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]]
>
>



R-help@stat.math.ethz.ch mailing list
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 08:57:44 2006

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