[R] SoS! How to predict new values using linear regression models?

[Petr Pikal]

Hi


On 29 Jan 2006 at 17:28, Gabor Grothendieck wrote:

Date sent:      	Sun, 29 Jan 2006 17:28:29 -0500
From:           	Gabor Grothendieck <ggrothendieck at gmail.com>
To:             	Michael <comtech.usa at gmail.com>
Copies to:      	R-help at stat.math.ethz.ch
Subject:        	Re: [R] SoS! How to predict new values using linear regression
	models?

> Leaving aside the issue of whether linear regression is appropriate
> here, do it like this where I have used the builtin iris data frame
> since I don't have access to your ss:
> 
> iris.lm <- lm(as.numeric(Species) ~ Sepal.Length + Sepal.Width, iris)
> predict(iris.lm, data.frame(Sepal.Length = 3, Sepal.Width = 2))
> 
> On 1/29/06, Michael <comtech.usa at gmail.com> wrote:
> > Hi all,
> >
> > After trial and error by myself for a few hours, I decide to ask for
> > your help.
> >
> > I have a training set which is a matrix of size 200 x 2, where the
> > two columns denote each independent variable. I have 200
> > observations.
> >
> > -----------------
> > ss=data.frame(trainingSet);
> > result=lm(trainingClass~ss$X1+ss$X2);
                                          ^^^^    ^^^

As Gabor suggested, use data argument.

result=lm(trainingClass~X1+X2, data=ss)

and your predict shall work.

HTH
Petr

> > -----------------
> >
> > where trainingClass denotes the true classes of the training data.
> >
> > Now I want to apply the model to predict new data:
> >
> > -----------------
> > > gg=predict(result, data.frame(X1=1, X2=2))
> > Warning message:
> > 'newdata' had 1 rows but variable(s) found have 200 rows
> > -----------------
> >
> > That's to say, I provide a new data which is one observation of 2
> > independent variables(1 row, two columns). I converted it into data
> > frame.
> >
> > However, the R never gives me new predication value for this NEW ONE
> > observation. Instead, it keeps giving me the above warning and keeps
> > printing the fitted value for the 200 training samples...
> >
> > That's very bad.
> >
> > Please help me!
> >
> >        [[alternative HTML version deleted]]
> >
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> >
> 
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Petr Pikal
petr.pikal at precheza.cz