recipes (version 0.1.0)

step_spatialsign: Spatial Sign Preprocessing

Description

step_spatialsign is a specification of a recipe step that will convert numeric data into a projection on to a unit sphere.

Usage

step_spatialsign(recipe, ..., role = "predictor", trained = FALSE,
  columns = NULL)

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 will be used for the normalization. See selections for more details.

role

For model terms created by this step, what analysis role should they be assigned?

trained

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

columns

A character string of variable names that will be (eventually) populated by the terms argument.

Value

An updated version of recipe with the new step added to the sequence of existing steps (if any).

Details

The spatial sign transformation projects the variables onto a unit sphere and is related to global contrast normalization. The spatial sign of a vector w is w/norm(w).

The variables should be centered and scaled prior to the computations.

References

Serneels, S., De Nolf, E., and Van Espen, P. (2006). Spatial sign preprocessing: a simple way to impart moderate robustness to multivariate estimators. Journal of Chemical Information and Modeling, 46(3), 1402-1409.

Examples

# NOT RUN {
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)

ss_trans <- rec %>%
  step_center(carbon, hydrogen) %>%
  step_scale(carbon, hydrogen) %>%
  step_spatialsign(carbon, hydrogen)

ss_obj <- prep(ss_trans, training = biomass_tr)

transformed_te <- bake(ss_obj, biomass_te)

plot(biomass_te$carbon, biomass_te$hydrogen)

plot(transformed_te$carbon, transformed_te$hydrogen)
# }