[R] small problem with predict

Rolf Turner rolf at math.unb.ca
Fri Jul 16 13:44:11 CEST 2004

You wrote:

> I have a small problem wit predict() for lm
> Let's say I have predictors x1 and x2, response y
> I want to predict for a new ds say
> dn<-data.frame(x1= seq(min(x1),max(x1),length=10),x2=rep(median(x2),10))
> predict(lm(y~x1+x2),dn,se.fit=T)
> Error message
> >  Error: variables 'x1', 'x2' were specified differently from the fit

	I tried your example (with a made-up ``original'' x1 and x2,
	and y) and got a perfectly reasonable result, with no error

	Explicitly I did:

	> x1 <- runif(42)
	> x2 <- rnorm(42)
	> y  <- 4 + 2*x1 + 3*x2 + rnorm(42)
	> dn <-data.frame(x1=seq(min(x1),max(x1),length=10),
	> predict(lm(y~x1+x2),dn,se.fit=T)

	No problema.

	Are you sure you did what you say you did?


						Rolf Turner
						rolf at math.unb.ca

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