Re: [R] Predicted value at a new level in lm

From: Gavin Simpson <gavin.simpson_at_ucl.ac.uk>
Date: Tue 17 Oct 2006 - 21:16:23 GMT

On Tue, 2006-10-17 at 12:34 -0700, Li Zhang wrote:
> Y X Z
> 42.0 7.0 33.0
> 33.0 4.0 41.0
> 75.0 16.0 7.0
> 28.0 3.0 49.0
> 91.0 21.0 5.0
> 55.0 8.0 31.0
>
>
> data<-read.table("d.txt",header=TRUE)
> mod<-lm(data$Y~data$X+data$Z)
> ---------------------------------------
>
> I would like to know the predict value at a new level,
> say
>
> X=10 Z=30

> dat <- scan()

1:    42.0    7.0   33.0
4:    33.0    4.0   41.0
7:    75.0   16.0    7.0
10:    28.0    3.0   49.0
13:    91.0   21.0    5.0

16: 55.0 8.0 31.0
19:
Read 18 items
> dat <- as.data.frame(matrix(dat, ncol = 3, byrow = TRUE))
> names(dat) <- c("X","Y","Z")
> dat

   X Y Z
1 42 7 33
2 33 4 41
3 75 16 7
4 28 3 49
5 91 21 5
6 55 8 31
> mod <- lm(Y ~ X + Z, data = dat) # note use of data argument
> pred <- predict(mod, newdata = list(X = 10, Z = 30))
> pred
[1] -0.003469617

or

> pred <- predict(mod, newdata = data.frame(X = 10, Z = 30))
> pred

[1] -0.003469617

HTH G

>
> Is there a function available to calculate it
> directly?
>
> Thank you
>
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Gavin Simpson                     [t] +44 (0)20 7679 0522
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Received on Wed Oct 18 07:35:51 2006

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