[R] Predictions with 'missing' variables

[Ista Zahn]

See the note in the help page for ?predict.glm

Best,
Ista

On Tue, Jan 25, 2011 at 2:59 PM, Axel Urbiz <axel.urbiz at gmail.com> wrote:
> Dear List,
>
> I think I'm going crazy here...can anyone explain why do I get the same
> predictions in train and test data sets below when the second has a missing
> input?
>
> y <- rnorm(1000)
> x1 <- rnorm(1000)
> x2 <- rnorm(1000)
> train <- data.frame(y,x1,x2)
> test <- data.frame(x1)
>
> myfit <- glm(y ~ x1 + x2, data=train)
> summary(myfit)
> all(predict(myfit, test) == predict(myfit, train))
>
> [1] TRUE
>
>
>
> Thanks,
>
> Axel.
>
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>
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-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org