recipes: step_scale – R documentation

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step_scale

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")
)

## S3 method for class 'step_scale'
tidy(x, ...)

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 which variables are affected by the step. See `selections()` for more details. For the `tidy` method, these are not currently used.
`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.recipe()`.
`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.recipe()`? While all operations are baked when `prep.recipe()` 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.
`x`	A `step_scale` object.

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 existing steps (if any). For the tidy method, a tibble with columns terms (the selectors or variables selected) and value (the standard deviations).

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.

Examples

library(modeldata)
data(biomass)

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)

recipes

Preprocessing Tools to Create Design Matrices

v0.1.16

MIT + file LICENSE

Authors

Max Kuhn [aut, cre], Hadley Wickham [aut], RStudio [cph]

Initial release