[R] simple predict question

Peter Alspach
Tue, 31 May 2005 21:16:38 -0000

Alternatively, one can convert dat to a data frame first (?lm states that data
is "an optional data frame containing the variables in the model."):

dat<-matrix(c(0,0,10,20),2,byrow=T)
dat <- as.data.frame(dat)
lm1<-lm(V2~V1, dat)
predict(lm1, data.frame(V1=seq(0,10,1)))
 1  2  3  4  5  6  7  8  9 10 11
 0  2  4  6  8 10 12 14 16 18 20

Cheers .........

Peter Alspach


>>> Gabor Grothendieck <ggrothendieck at gmail.com> 01/06/05
09:00:15 >>>
On 5/31/05, sms13+ at pitt.edu <sms13+ at pitt.edu>
wrote:
> Excuse the simple question...
> I'm not sure what I'm doing wrong with predict, but let me use this
example:
> Suppose I do:
> dat<-matrix(c(0,0,10,20),2,byrow=T)
> lm1<-lm(dat[,2]~dat[,1])
>
> Suppose I want to generate the linearly-interpolated y-values between the
> point (0,0) and (0,20) at every unit interval.
> I thought I just do:
> predict(lm1, data.frame(seq(0,10,1))) to get 0,2,4,6...,18,20, but instead
> I just get:
> 1    2
> 0  20
>

I think the names are confusing it.  Try:

x <- dat[,1]; y <- dat[,2]
lm1 <- lm(y ~ x)
predict(lm1, data.frame(x = 1:10))

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