R/TaskOrdinal.R

In mlr-org/mlr3ordinal: Ordinal regression for mlr3

#' @title Ordinal Task
#'
#' @name TaskOrdinal
#' @format [R6Class] object inheriting from [mlr3::Task]/[mlr3::TaskSupervised].
#' @description
#' This task specializes [mlr3::Task] and [mlr3::TaskSupervised] for ordinal regression problems.
#'
#' @section Usage:
#' Inherits from [mlr3::Task]/[mlr3::TaskSupervised].
#' ```
#' # Construction
#' t = TaskSupervised$new(id, backend, target)
#'
#' @examples
#' library(mlr3)
#' # ...
NULL

#' @export
TaskOrdinal = R6Class("TaskOrdinal",
  inherit = mlr3::TaskSupervised,
  public = list(
    initialize = function(id, backend, target) {
      assert_string(target)
      super$initialize(id = id, task_type = "ordinal", backend = backend, target = target)

      info = self$col_info[id == target]
      levels = info$levels[[1L]]

      if ("ordered" %nin% c(info$type)) {
        stopf("Target column '%s' must be an ordered factor", target)
      }
      if (length(levels) < 2L) {
        stopf("Target column '%s' must have at least two levels", target)
      }
    },

    truth = function(rows = NULL) {
      res = self$data(rows, cols = self$target_names)[[1L]]
      as_factor(res, levels = self$rank_names, ordered = TRUE)
    }
  ),

  active = list(
    rank_names = function() {
      self$col_info[list(self$target_names), "levels", with = FALSE][[1L]][[1L]]
    },

    rank_n = function() uniqueN(self$truth())
  )
)