R/PipeOpExplicitPta.R

In mlr3fairness: Fairness Auditing and Debiasing for 'mlr3'

#' @title PipeOpExplicitPta
#' 
#' @usage NULL
#' @name mlr_pipeops_explicit_pta
#' @format [R6Class] object inheriting from [`PipeOpTaskPreproc`]/[`PipeOp`].
#'
#' @description
#'   Turns the column with column role 'pta' into an explicit separate column prefixed with ".._internal_pta_".
#'   This keeps it from getting changed or adapted by subsequent pipelines that operate on the feature pta.
#' 
#' @section Construction:
#' ```
#' PipeOpExplicitPta$new(id = "reweighing", param_vals = list())
#' ```
#' * `id` (`character(1)`).
#' * `param_vals` (`list()`)
#' 
#' @section Input and Output Channels:
#' Input and output channels are inherited from [PipeOpTaskPreproc]. Instead of a [Task][mlr3::Task], a
#' [TaskClassif][mlr3::TaskClassif] is used as input and output during training and prediction.
#'
#' The output during training is the input [Task][mlr3::Task] with added weights column according
#' to target class. The output during prediction is the unchanged input.
#'
#
#' @section State:
#' The `$state` is a named `list` with the `$state` elements inherited from [PipeOpTaskPreproc][mlr3pipelines::PipeOpTaskPreproc].
#'
#' @section Parameters:
#' The PipeOp does not have any hyperparameters.
#' 
#' @section Internals:
#' Copies the existing pta column to a new column.
#' 
#' @section Fields:
#' Only fields inherited from [PipeOpTaskPreproc]/[`PipeOp`].
#'
#' @section Methods:
#' Methods inherited from [PipeOpTaskPreproc][mlr3pipelines::PipeOpTaskPreproc]/[PipeOp][mlr3pipelines::PipeOp].
#' 
#' @family PipeOps
#' @seealso https://mlr3book.mlr-org.com/list-pipeops.html
#' @export
#' @examples
#' library("mlr3")
#' library("mlr3pipelines")
#' epta = po("explicit_pta")
#' new = epta$train(list(tsk("adult_train")))
PipeOpExplicitPta = R6Class("PipeOpExplicitPta",
  inherit = PipeOpTaskPreproc,
  public = list(
    #' @description
    #' Creates a new instance of this [R6][R6::R6Class][PipeOp] R6 class.
    #'
    #' @param id `character` \cr
    #'   The PipeOps identifier in the PipeOps library.
    #' @param param_vals `list` \cr
    #'   The parameter values to be set. See `Parameters`.
    initialize = function(id = "explicit_pta", param_vals = list()) {
      super$initialize(id, param_set = ParamSet$new(), param_vals = param_vals)
    }
  ),

  private = list(
    .train_task = function(task) {
        private$.transform_task(task)
    },

    .predict_task = function(task) {
        private$.transform_task(task)
    },

    .transform_task = function(task) {
      assert_pta_task(task)
      pta = task$col_roles$pta
      if (any(startsWith(task$feature_names, "..internal_pta"))) {
          stop("Task already has an explicit ..internal_pta column")
      }
      dt = task$data(cols = c(task$backend$primary_key, pta))
      newpta = paste0("..internal_pta_", pta)
      setnames(dt, pta, newpta)
      task$cbind(dt)
      task$set_col_roles(newpta, "pta")  
      task$set_col_roles(pta, remove_from =  "pta")  
      return(task)
    }
  )
)