step_scale {recipes}

Scaling numeric data

Description

step_scale() creates a specification of a recipe step that will normalize numeric data to have a standard deviation of one.

Usage

step_scale(
  recipe,
  ...,
  role = NA,
  trained = FALSE,
  sds = NULL,
  factor = 1,
  na_rm = TRUE,
  skip = FALSE,
  id = rand_id("scale")
)

Arguments

recipe

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.

role

Not used by this step since no new variables are created.

trained

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

sds

A named numeric vector of standard deviations. This is NULL until computed by prep().

factor

A numeric value of either 1 or 2 that scales the numeric inputs by one or two standard deviations. By dividing by two standard deviations, the coefficients attached to continuous predictors can be interpreted the same way as with binary inputs. Defaults to 1. More in reference below.

na_rm

A logical value indicating whether NA values should be removed when computing the standard deviation.

skip

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.

id

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

Details

Scaling data means that the standard deviation of a variable is divided out of the data. step_scale estimates the variable standard deviations from the data used in the training argument of prep.recipe. bake.recipe then applies the scaling to new data sets using these standard deviations.

Value

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

Tidying

When you tidy() this step, a tibble is returned with columns terms, value , and id:

terms

character, the selectors or variables selected

value

numeric, the standard deviations

id

character, id of this step

Case weights

This step performs an unsupervised operation that can utilize case weights. As a result, case weights are only used with frequency weights. For more information, see the documentation in case_weights and the examples on tidymodels.org.

References

Gelman, A. (2007) "Scaling regression inputs by dividing by two standard deviations." Unpublished. Source: http://www.stat.columbia.edu/~gelman/research/unpublished/standardizing.pdf.

See Also

Other normalization steps: step_center(), step_normalize(), step_range()

Examples

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
)

scaled_trans <- rec %>%
  step_scale(carbon, hydrogen)

scaled_obj <- prep(scaled_trans, training = biomass_tr)

transformed_te <- bake(scaled_obj, biomass_te)

biomass_te[1:10, names(transformed_te)]
transformed_te
tidy(scaled_trans, number = 1)
tidy(scaled_obj, number = 1)