Create linear splines basis — make

This function creates the basis function of a second-order (linear) splines at a user-specific set of break points.

Usage

make_basis(
  x,
  xname = "x",
  internal = NULL,
  boundary = range(x),
  degree = 1L,
  warn = TRUE
)

x: numeric vector
xname: predictor name. Default is "x"
internal: a vector of internal knots, excluding boundary knots
boundary: vector of external knots
degree: the degree of the spline. The broken stick model requires linear splines, so the default is degree = 1. Setting degree = 0 yields (crisp) dummy coding, and one column less than for degree = 1.
warn: a logical indicating whether warnings from splines::bs() should be given.

A matrix with length(x) rows and length(breaks)

columns, with some extra attributes described by bs().

Before version 0.54, it was standard practice that the knots array always included boundary[1L].

Stef van Buuren 2023