R/MeasureSelectedFeatures.R

In mllg/mlr3: Machine Learning in R - Next Generation

#' @title Selected Features Measure
#'
#' @usage NULL
#' @aliases mlr_measures_selected_features
#' @format [R6::R6Class()] inheriting from [Measure].
#' @include Measure.R
#'
#' @section Construction:
#' ```
#' MeasureSelectedFeatures$new(normalize = FALSE)
#' mlr_measures$get("selected_features")
#' msr("selected_features")
#' ```
#'
#' * `normalize` :: `logical(1)`\cr
#' If `normalize` is set to `TRUE`, divides the number of features by the total number of features.
#'
#' @description
#' Measures the number of selected features.
#'
#' @template seealso_measure
#' @export
MeasureSelectedFeatures = R6Class("MeasureSelectedFeatures",
  inherit = Measure,
  public = list(
    normalize = NULL,

    initialize = function(normalize = FALSE) {
      super$initialize(
        id = "selected_features",
        task_type = NA_character_,
        properties = c("requires_task", "requires_learner"),
        predict_type = "response",
        range = c(0, Inf),
        minimize = TRUE
      )
      self$normalize = assert_flag(normalize)
    },

    score_internal = function(prediction, task, learner, ...) {
      if ("selected_features" %nin% learner$properties) {
        return(NA_integer_)
      }
      n = length(learner$selected_features())
      if (self$normalize) {
        n = n / length(task$feature_names)
      }
      n
    }
  )
)

#' @include mlr_measures.R
mlr_measures$add("selected_features", MeasureSelectedFeatures)