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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
)

Arguments

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.

Value

A matrix with length(x) rows and length(breaks)columns, with some extra attributes described by bs().

Note

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

Author

Stef van Buuren, 2020