step_bs: B-Spline Basis Functions

View source: R/bs.R

step_bsR Documentation

B-Spline Basis Functions


step_bs() creates a specification of a recipe step that will create new columns that are basis expansions of variables using B-splines.


  role = "predictor",
  trained = FALSE,
  deg_free = NULL,
  degree = 3,
  objects = NULL,
  options = list(),
  keep_original_cols = FALSE,
  skip = FALSE,
  id = rand_id("bs")



A recipe object. The step will be added to the sequence of operations for this recipe.


One or more selector functions to choose variables for this step. See selections() for more details.


For model terms created by this step, what analysis role should they be assigned? By default, the new columns created by this step from the original variables will be used as predictors in a model.


A logical to indicate if the quantities for preprocessing have been estimated.


The degrees of freedom for the spline. As the degrees of freedom for a spline increase, more flexible and complex curves can be generated. When a single degree of freedom is used, the result is a rescaled version of the original data.


Degree of polynomial spline (integer).


A list of splines::bs() objects created once the step has been trained.


A list of options for splines::bs() which should not include x, degree, or df.


A logical to keep the original variables in the output. Defaults to FALSE.


A logical. Should the step be skipped when the recipe is baked by bake()? While all operations are baked when prep() is run, some operations may not be able to be conducted on new data (e.g. processing the outcome variable(s)). Care should be taken when using skip = TRUE as it may affect the computations for subsequent operations.


A character string that is unique to this step to identify it.


step_bs can create new features from a single variable that enable fitting routines to model this variable in a nonlinear manner. The extent of the possible nonlinearity is determined by the df, degree, or knot arguments of splines::bs(). The original variables are removed from the data and new columns are added. The naming convention for the new variables is varname_bs_1 and so on.


An updated version of recipe with the new step added to the sequence of any existing operations.


When you tidy() this step, a tibble with column terms (the columns that will be affected) is returned.

Tuning Parameters

This step has 2 tuning parameters:

  • deg_free: Spline Degrees of Freedom (type: integer, default: NULL)

  • degree: Polynomial Degree (type: integer, default: 3)

Case weights

The underlying operation does not allow for case weights.

See Also

Other individual transformation steps: step_BoxCox(), step_YeoJohnson(), step_harmonic(), step_hyperbolic(), step_inverse(), step_invlogit(), step_logit(), step_log(), step_mutate(), step_ns(), step_percentile(), step_poly(), step_relu(), step_sqrt()


data(biomass, package = "modeldata")

biomass_tr <- biomass[biomass$dataset == "Training", ]
biomass_te <- biomass[biomass$dataset == "Testing", ]

rec <- recipe(
  HHV ~ carbon + hydrogen + oxygen + nitrogen + sulfur,
  data = biomass_tr

with_splines <- rec %>%
  step_bs(carbon, hydrogen)
with_splines <- prep(with_splines, training = biomass_tr)

expanded <- bake(with_splines, biomass_te)

recipes documentation built on Aug. 26, 2023, 1:08 a.m.