makepredictcall
Utility Function for Safe Prediction
A utility to help model.frame.default create the right
matrices when predicting from models with terms like (univariate)
poly or ns.
- Keywords
- models
Usage
makepredictcall(var, call)Arguments
- var
A variable.
- call
The term in the formula, as a call.
Details
This is a generic function with methods for poly, bs and
ns: the default method handles scale. If
model.frame.default encounters such a term when
creating a model frame, it modifies the predvars attribute of
the terms supplied by replacing the term with one which will work for
predicting new data. For example makepredictcall.ns adds
arguments for the knots and intercept.
To make use of this, have your model-fitting function return the
terms attribute of the model frame, or copy the predvars
attribute of the terms attribute of the model frame to your
terms object.
To extend this, make sure the term creates variables with a class, and write a suitable method for that class.
Value
A replacement for call for the predvars attribute of
the terms.
See Also
model.frame, poly, scale;
bs and ns in package splines.
cars for an example of prediction from a polynomial fit.
Examples
library(stats)
# NOT RUN {
require(graphics)
## using poly: this did not work in R < 1.5.0
fm <- lm(weight ~ poly(height, 2), data = women)
plot(women, xlab = "Height (in)", ylab = "Weight (lb)")
ht <- seq(57, 73, len = 200)
nD <- data.frame(height = ht)
pfm <- predict(fm, nD)
lines(ht, pfm)
pf2 <- predict(update(fm, ~ stats::poly(height, 2)), nD)
stopifnot(all.equal(pfm, pf2)) ## was off (rel.diff. 0.0766) in R <= 3.5.0
## see also example(cars)
## see bs and ns for spline examples.
# }