[R] Forcing coefficients in lm object

Henrique Dallazuanna
Tue, 28 Aug 2007 13:44:16 -0000

Hi,

names(fit)
fit$coefficients[[2]] <- 100

--
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25'' 40" S 49° 16'' 22" O

On 28/08/07, J.J.P.Lebrec@lumc.nl <J.J.P.Lebrec@lumc.nl>
wrote:
>
> Dear all,
>
> I would like to use predict.lm() with an existing lm object but with new
> arbitrary coefficients. I modify ''fit$coef'' (see example
below) "by hand"
> but the actual model in ''fit'' used for prediction does
not seem to be
> altered (although fit$coef is!).
>
> Can anyone please help me do this properly?
>
> Thanks in advance,
>
> Jérémie
>
>
>
> > dat <- data.frame(y=c(0,25,32,15), x=as.factor(c(1,1,2,2)))
> > fit <- lm(y ~ x, data=dat)
> > fit
>
> Call:
> lm(formula = y ~ x, data = dat)
>
> Coefficients:
> (Intercept)           x2
>        12.5         11.0
>
> > fit$coef[[2]] <- 100
> > dat.new <- data.frame(x=as.factor(c(1,2,1,2)))
> > predict.lm(fit, dat.new)
>    1    2    3    4
> 12.5 23.5 12.5 23.5
> > fit
>
> Call:
> lm(formula = y ~ x, data = dat)
>
> Coefficients:
> (Intercept)           x2
>        12.5         11.0
>
> > fit$coef
> (Intercept)          x2
>        12.5       100.0
> >
>
>
>
> Jérémie Lebrec
> Dept. of Medical Statistics and Bioinformatics
> Leiden University Medical Center
> Postzone S-05-P
> P.O. Box 9600
> 2300 RC Leiden
> The Netherlands
> j.j.p.lebrec@lumc.nl
>
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>

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