Extracting the knots of a natural cubic spline fit
On Mar 12, 2013, at 2:59 PM, Rajat Tayal <rajat at igidr.ac.in> wrote:
Dear list members, I am trying to fit a natural cubic spline to my dataset using the ns function in the splines package. Specifically, I do: library(splines) lm(y ~ ns(x, df=3), data =data) How do I extract the values of the interior knots of the fitted spline ? Thanks, Rajat
Using the example from ?ns: require(splines) fm1 <- lm(weight ~ ns(height, df = 5), data = women)
attr(terms(fm1), "predvars")
list(weight, ns(height, knots = c(60.8, 63.6, 66.4, 69.2), Boundary.knots = c(58, 72), intercept = FALSE)) or directly on the data:
attr(ns(women$height, df = 5), "knots")
20% 40% 60% 80% 60.8 63.6 66.4 69.2
attr(ns(women$height, df = 5), "Boundary.knots")
[1] 58 72 Regards, Marc Schwartz