[R] Question about predict function

[Chuck Cleland]

Thomas L Jones wrote:
> I am working with a non-parametic smoothing operation using a 
> Generalized Additive Model. It is a bivariate data set. I know how to 
> do the smooth, and out comes a nice smooth curve.
> 
> Now I want to find the value of the smoothed curve for several values 
> of x (the abscissa). This can be done (please correct me if I am 
> wrong) by using the predict.gam function. You feed the predict.gam 
> function a data frame, telling it what you want.
> 
> Let's start with the predict.gam function. Are you supposed to be able 
> to look up how to use it? E.g., what goes into the various columns of 
> the data frame? I do have a working function call for predict. It 
> says:
> 
> pred_out <- predict (mod, data.frame (x = x), type = "response")
> 
> (mod is the model)
> 
> Now, if you tell me that x = x, I will believe you. But what is meant 
> by "data.frame (x = x)", I know not.
> 
> Or would it better to call the class, names, and str functions, using 
> some well chosen objects?

  Does this help?

library(gam)
data(kyphosis)

kyphosis.gam <- gam(Kyphosis ~ s(Age,4) + Number, family = binomial,
data=kyphosis)

predict(kyphosis.gam, data.frame(Age = c(10,100,200), Number = 3),
type="response")

          1           2           3
0.019098701 0.248043366 0.005807921

  The data frame should contain the predictor variables in the model and
the values for the variables should be those at which you want a prediction.

> Tom Jones
> 
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-- 
Chuck Cleland, Ph.D.
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