compute_score.R

#' Scoring utility
#'
#' Computes the relation of score before a change (e.g. [PFI], [LOCO], ...) and after.
#'
#' If `minimize == TRUE`, then `scores_post - scores_pre` is computed for
#' `relation == "difference"`, otherwise `scores_pre - scores_post` is given.
#' If `minimize == FALSE`, then `scores_pre - scores_post` is computed.
#'
#' @param scores_pre (numeric()) Score before change.
#' @param scores_post (numeric()) Score after change.
#' @param relation (character(1), `"difference"`) Either `"difference"` or `"ratio"`.
#'  If `"difference"`, then `scores_post - scores_pre` is computed, otherwise `scores_post / scores_pre`.
#' @param minimize (logical(1), `TRUE`) Whether the score needs to be minimized (e.g. RMSE) or
#' maximized (e.g. AUC).
#'
#' @return A numeric vector of the same length as `scores_pre` and `scores_post`
#' @export
#'
#' @examples
#'
#' pre = rnorm(10)
#' post = pre + runif(10)
#'
#' compute_score(pre, post)
#' compute_score(pre, post, "ratio")
#' compute_score(pre, post, minimize = FALSE)
compute_score = function(scores_pre, scores_post,
                         relation = c("difference", "ratio"),
                         minimize = TRUE) {
  checkmate::assert_numeric(scores_pre, any.missing = FALSE)
  checkmate::assert_numeric(scores_post, any.missing = FALSE)
  checkmate::assert_true(length(scores_pre) == length(scores_post))
  checkmate::assert_flag(minimize)
  relation = match.arg(relation)

  if (minimize) {
    # Lower is better, e.g. ce
    switch(relation,
      difference = scores_post - scores_pre,
      ratio = scores_post / scores_pre
    )
  } else {
    # Higher is better, e.g. accuracy
    switch(relation,
      difference = scores_pre - scores_post,
      ratio = scores_pre / scores_post
    )
  }
}