It is fit$coefficients, not fit$coef .
From the help page:
name: A literal character string or a name (possibly backtick
quoted). For extraction, this is normally (see under
Environments) partially matched to the 'names' of the object.
Note the qualifier 'for extraction', so you assigned a new element with
name 'coef', and predict.lm used fit$coefficients.
On Tue, 28 Aug 2007, [EMAIL PROTECTED] wrote:
Dear all,
I would like to use predict.lm() with an existing lm object but with new arbitrary
coefficients. I modify 'fit$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
[EMAIL PROTECTED]
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--
Brian D. Ripley, [EMAIL PROTECTED]
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
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