R/ifw.R

In egenn/rtemis: Machine Learning and Visualization

# ifw.R
# ::rtemis::
# 2025 EDG rtemis.org

#' Inverse Frequency Weighting
#'
#' @param y Vector: Outcome
#'
#' @keywords internal
#' @noRd
#' @author EDG
#'
#' @examples
#' \dontrun{
#' y <- factor(sample(c("A", "B"), size = 1000, replace = 1000, prob = c(.1, .9)))
#' ifw(y)
#' ifw(y, type = "case_weights")
#' }
ifw <- function(y, type = c("case_weights", "class_weights"), verbosity = 1L) {
  stopifnot(is.factor(y))
  type <- match.arg(type)
  if (verbosity > 0L) {
    msg20(
      "Using Inverse Frequency Weighting to calculate ",
      sub("_", " ", type),
      "."
    )
  }

  # Class weights ----
  inverse_proportions <- 1 / (table(y) / NROW(y))
  class_weights <- structure(
    inverse_proportions / min(inverse_proportions),
    names = levels(y)
  )

  if (type == "class_weights") {
    out <- class_weights
    stopifnot(length(out) == length(levels(y)))
  } else {
    out <- class_weights[as.integer(y)]
    stopifnot(length(out) == length(y))
  }
  out
} # /rtemis::ifw