[R] extract hyperplan from e1071 model

[Sarah Goslee]

Hi,

Please don't forget to copy R-help on your reply - other people are
likely to have more insight.

My understanding is that you want to replicate the shaded polygons
produced by plot.svm on your own plot. That's why I suggested you
first try add=TRUE, and if that doesn't work, then look at the code
for plot.svm so you can see how the predicted values are calculated on
a grid to be plotted. R is open source - you can extract the section
from that function that does what you want, and make your own code to
add it to another plot.

I have no idea what "the tutorial" is; I suggested two things you
could try based on the help and my understanding of R.

Sarah

On Thu, Dec 20, 2018 at 9:07 AM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>
> Dear Sarah,
> I have looked at the tutorial but I did not find what I was looking
> for. Essentially, I would like to extract the data that make the
> hyperplane (it should be a matrix of X,Y value, for a bidimensional
> plane, I guess) so I can plot a line in another plot. I tried with
> model$SV but it is not the right one.
> Luigi
>
> On Thu, Dec 20, 2018 at 2:59 PM Sarah Goslee <sarah.goslee using gmail.com> wrote:
> >
> > Hi,
> >
> > According to the help for svm, which you probably should have started
> > with, SV contains the support vectors, and index contains the position
> > of the support vectors in the data matrix.
> >
> > As for plotting, plot.svm lets you pass additional options to plot so
> > that you can customize the plot to your tastes. I'm not sure if
> > add=TRUE is a useful option there, but you should try it. If that
> > doesn't meet your needs, R is open source - you can easily look at the
> > code for plot.svm and see what you need (basically the predicted
> > values on agrid, if I'm understanding your goal correctly).
> >
> > Sarah
> >
> > On Thu, Dec 20, 2018 at 5:16 AM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
> > >
> > > Dear all,
> > > I am using the package e1071 for modeling SVM. I obtain a model from
> > > the data and I can plot the results; the plot shows the support
> > > vectors (as 'X's) and the shaded areas as it should be.
> > > However, I don't like the plot generated from the model and I would
> > > like instead to have more control upon the plotting; in particular, I
> > > would like to draw the hyperplane on plots I have already made from
> > > the data available.
> > > Is there a way to extract the values that are used to draw the hyperplane?
> > > That is: plot(model) -- where model is obtained from svm() -- draws an
> > > area in blue and one in red based on some values provided by model;
> > > can I get these values so I can plot a line in a pre-existing plot?
> > > Also, it is possible to extract the positions of the support vectors?
> > > The names of the model generated by svm() are:
> > > > names(mod)
> > >  [1] "call"            "type"            "kernel"          "cost"
> > >  [5] "degree"          "gamma"           "coef0"           "nu"
> > >  [9] "epsilon"         "sparse"          "scaled"          "x.scale"
> > > [13] "y.scale"         "nclasses"        "levels"          "tot.nSV"
> > > [17] "nSV"             "labels"          "SV"              "index"
> > > [21] "rho"             "compprob"        "probA"           "probB"
> > > [25] "sigma"           "coefs"           "na.action"       "fitted"
> > > [29] "decision.values" "terms"
> > >
> > > Which one should I look at?
> > > Thank you
> > > --
> > > Best regards,
> > > Luigi
> > >



-- 
Sarah Goslee (she/her)
http://www.numberwright.com