step_bs() creates a specification of a recipe step that will create new
columns that are basis expansions of variables using B-splines.
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.
An updated version of recipe with the new step added to the
sequence of any existing operations.
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 knots 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.
When you tidy() this step, a tibble is returned with
columns terms and id:
character, the selectors or variables selected
character, id of this step
This step has 2 tuning parameters:
deg_free: Spline Degrees of Freedom (type: integer, default: NULL)
degree: Polynomial Degree (type: integer, default: 3)
The underlying operation does not allow for case weights.
Other individual transformation steps:
step_BoxCox(),
step_YeoJohnson(),
step_harmonic(),
step_hyperbolic(),
step_inverse(),
step_invlogit(),
step_log(),
step_logit(),
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)
expanded
#> # A tibble: 80 × 10
#> oxygen nitrogen sulfur HHV carbon_bs_1 carbon_bs_2 carbon_bs_3
#> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1 47.2 0.3 0.22 18.3 0.437 0.273 0.0568
#> 2 48.1 2.85 0.34 17.6 0.444 0.236 0.0417
#> 3 49.1 2.4 0.3 17.2 0.444 0.229 0.0394
#> 4 37.3 1.8 0.5 18.9 0.437 0.273 0.0571
#> 5 42.8 0.2 0 20.5 0.427 0.301 0.0707
#> 6 41.7 0.7 0.2 18.5 0.442 0.248 0.0465
#> 7 54.1 1.19 0.51 15.1 0.440 0.184 0.0256
#> 8 33.8 0.95 0.2 16.2 0.444 0.222 0.0369
#> 9 31.1 0.14 4.9 11.1 0.359 0.0771 0.00552
#> 10 23.7 4.63 1.05 10.8 0.338 0.0643 0.00408
#> # ℹ 70 more rows
#> # ℹ 3 more variables: hydrogen_bs_1 <dbl>, hydrogen_bs_2 <dbl>,
#> # hydrogen_bs_3 <dbl>