[R] Names of variables needed in newdata for predict.glm

[Bendix Carstensen]

I would like to extract the names, modes [numeric/factor] and levels
of variables needed in a data frame supplied as newdata= argument to
predict.glm()

Here is a small example illustrating my troubles; what I want from
(both of) the glm objects is the vector c("x","f","Y") and an
indication that f is a factor:

library( splines )
dd <- data.frame( D = sample(0:1,200,rep=T),
                  x = abs(rnorm(200)),
                  f = factor(sample(letters[1:4],200,rep=T)),
                  Y = runif(200,0.5,10) )
mx <- glm( D ~ ns(x,knots=1:2,Bo=c(0,5)) + f:I(x^2) , offset=log(Y) , family=poisson, data=dd)
mi <- glm( D ~ ns(x,knots=1:2,Bo=c(0,5)) + f:I(x^2) + offset(log(Y)), family=poisson, data=dd)

attr(mx$terms,"dataClasses")
attr(mi$terms,"dataClasses")
mi$xlevels
mx$xlevels

...so far not quite there.

Regards,

Bendix Carstensen

Senior Statistician
Steno Diabetes Center
Clinical Epidemiology
Niels Steensens Vej 2-4
DK-2820 Gentofte, Denmark
b at bxc.dk
bendix.carstensen at regionh.dk
http://BendixCarstensen.com

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