| predict.smooth.spline {stats} | R Documentation |
Predict a smoothing spline fit at new points, return the derivative if desired. The predicted fit is linear beyond the original data.
## S3 method for class 'smooth.spline' predict(object, x, deriv = 0, ...)
object |
a fit from |
x |
the new values of x. |
deriv |
integer; the order of the derivative required. |
... |
further arguments passed to or from other methods. |
A list with components
x |
The input |
y |
The fitted values or derivatives at |
require(graphics)
attach(cars)
cars.spl <- smooth.spline(speed, dist, df = 6.4)
## "Proof" that the derivatives are okay, by comparing with approximation
diff.quot <- function(x, y) {
## Difference quotient (central differences where available)
n <- length(x); i1 <- 1:2; i2 <- (n-1):n
c(diff(y[i1]) / diff(x[i1]), (y[-i1] - y[-i2]) / (x[-i1] - x[-i2]),
diff(y[i2]) / diff(x[i2]))
}
xx <- unique(sort(c(seq(0, 30, by = .2), kn <- unique(speed))))
i.kn <- match(kn, xx) # indices of knots within xx
op <- par(mfrow = c(2,2))
plot(speed, dist, xlim = range(xx), main = "Smooth.spline & derivatives")
lines(pp <- predict(cars.spl, xx), col = "red")
points(kn, pp$y[i.kn], pch = 3, col = "dark red")
mtext("s(x)", col = "red")
for(d in 1:3){
n <- length(pp$x)
plot(pp$x, diff.quot(pp$x,pp$y), type = "l", xlab = "x", ylab = "",
col = "blue", col.main = "red",
main = paste0("s" ,paste(rep("'", d), collapse = ""), "(x)"))
mtext("Difference quotient approx.(last)", col = "blue")
lines(pp <- predict(cars.spl, xx, deriv = d), col = "red")
points(kn, pp$y[i.kn], pch = 3, col = "dark red")
abline(h = 0, lty = 3, col = "gray")
}
detach(); par(op)