recipes: step_novel – R documentation

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step_novel

Simple Value Assignments for Novel Factor Levels

Description

step_novel creates a specification of a recipe step that will assign a previously unseen factor level to a new value.

Usage

step_novel(
  recipe,
  ...,
  role = NA,
  trained = FALSE,
  new_level = "new",
  objects = NULL,
  skip = FALSE,
  id = rand_id("novel")
)

## S3 method for class 'step_novel'
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 that will be affected by the step. These variables should be character or factor types. 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.
`new_level`	A single character value that will be assigned to new factor levels.
`objects`	A list of objects that contain the information on factor levels that will be determined by `prep.recipe()`.
`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_novel` object.

Details

The selected variables are adjusted to have a new level (given by new_level) that is placed in the last position. During preparation there will be no data points associated with this new level since all of the data have been seen.

Note that if the original columns are character, they will be converted to factors by this step.

Missing values will remain missing.

If new_level is already in the data given to prep, an error is thrown.

When fitting a model that can deal with new factor levels, consider using workflows::add_recipe() with allow_novel_levels = TRUE set in hardhat::default_recipe_blueprint(). This will allow your model to handle new levels at prediction time, instead of throwing warnings or errors.

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 columns that will be affected) and value (the factor levels that is used for the new value)

Examples

library(modeldata)
data(okc)

okc_tr <- okc[1:30000,]
okc_te <- okc[30001:30006,]
okc_te$diet[3] <- "cannibalism"
okc_te$diet[4] <- "vampirism"

rec <- recipe(~ diet + location, data = okc_tr)

rec <- rec %>%
  step_novel(diet, location)
rec <- prep(rec, training = okc_tr)

processed <- bake(rec, okc_te)
tibble(old = okc_te$diet, new = processed$diet)

tidy(rec, 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