[R] small problem with predict

[Rolf Turner]

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
	message.

	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),
                          x2=rep(median(x2),10))
	> predict(lm(y~x1+x2),dn,se.fit=T)

	No problema.

	Are you sure you did what you say you did?

					cheers,

						Rolf Turner
						rolf at math.unb.ca