[R] Re: trouble with prcomp()

[Scott Robbins Loarie]

Brilliant!

Thanks so much for the help!

-Scott

On Mon, 14 Jun 2004, Prof Brian Ripley wrote:

> Centring and scaling.  The code is very easy to real, and contains
>
>     x <- as.matrix(x)
>     x <- scale(x, center = center, scale = scale.)
>
> Note that the help page does say
>
>      The calculation is done by a singular value decomposition of the
>      (centered and scaled) data matrix ....
>
>
> On Mon, 14 Jun 2004, Scott Robbins Loarie wrote:
>
> > Thanks very much for showing me these functions,
> >
> > In prcomp(), the documentation says that Value: x is "the data
> > multiplied by the 'rotation' matix".  Using sample data:
> >
> > data(iris)
> > iris<-as.matrix(iris[,1:4])
> > pcprim<-prcomp(iris, scale=TRUE)
> >
> > Why does iris%*%pcprim$rotation (the data multiplied by the rotation
> > matrix) not equal pcprim$x?
> >
> > Thanks very much,
> >
> > Scott
> >
> >
> > On Mon, 14 Jun 2004, Prof Brian Ripley wrote:
> >
> > > Why are you using the OPRHANED multiv library for a facility covered by
> > > princomp() and prcomp() in base R?  The list might be able to help you
> > > with the latter, but no one is supporting multiv (hence its status).
> > >
> > > On Sun, 13 Jun 2004, Scott Robbins Loarie wrote:
> > >
> > > > I am having trouble using the pca function in the multiv library.
> > > > I am trying to generate the values found in $rproj by using $evecs to
> > > > calculate linear combinations of my input data.  However, I have been not
> > > > been able to correctly calculate the $rproj values.
> > > >
> > > > Using the following standard sample data, why does iris%*%pcprim$evecs[,]
> > > > not equal pcprim$rproj?
> > > >
> > > > data(iris)
> > > > iris<-as.matrix(iris[,1:4])
> > > > pcprim<-pca(iris)
> > >
> > > --
> > > Brian D. Ripley,                  ripley at stats.ox.ac.uk
> > > Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> > > University of Oxford,             Tel:  +44 1865 272861 (self)
> > > 1 South Parks Road,                     +44 1865 272866 (PA)
> > > Oxford OX1 3TG, UK                Fax:  +44 1865 272595
> > >
> >
> >
>
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>