add methods to calculate nadir and ideal points from a set of points

NAMESPACE

@@ -8,6 +8,8 @@ S3method(getSupportedRepresentations,ecr_operator)
 S3method(is.supported,ecr_operator)
 S3method(print,ecr_control)
 S3method(print,ecr_result)
+export(approximateIdealPoint)
+export(approximateNadirPoint)
 export(computeAverageHausdorffDistance)
 export(computeCrowdingDistance)
 export(computeDominatedHypervolume)

R/approximatePoints.R

@@ -0,0 +1,70 @@
+#' Reference point approximations.
+#'
+#' Helper functions to compute nadir or ideal point from sets of points, e.g.,
+#' multiple approxiamtion sets.
+#'
+#' @param ... [any]\cr
+#'   Sets as matrizes.
+#' @param sets [\code{list}]\cr
+#'   List of sets. This is an alternative way of passing the sets. Can be used
+#'   exclusively or combined with \code{...}.
+#' @return [numeric] Reference point.
+#' @export
+#' @rdname reference_point_approximation
+approximateNadirPoint = function(..., sets = NULL) {
+  return(approximatePoint(..., sets = sets, FUN = max))
+}
+
+#' @export
+#' @rdname reference_point_approximation
+approximateIdealPoint = function(..., sets = NULL) {
+  return(approximatePoint(..., sets = sets, FUN = min))
+}
+
+# Helper to compute the Nadir point.
+#
+# The nadir point is constructed by the worst objective values of the
+# concatenation of all given point sets.
+#
+# @param ... [any]\cr
+#   Sets as matrizes.
+# @param sets [\code{list}]\cr
+#   List of sets. This is an alternative way of passing the sets. Can be used
+#   exclusively or combined with \code{...}.
+# @param FUN [\code{function}]\cr
+#   Either min or max function.
+# @return [numeric]
+approximatePoint = function(..., sets = NULL, FUN) {
+  assertFunction(FUN)
+
+  # we can combine both types of parameter passing here
+  sets2 = list(...)
+  if (!is.null(sets)) {
+    assertList(sets, types = "matrix")
+  }
+  sets = c(sets, sets2)
+  assertListOfPointSets(sets)
+
+  # sapply returns a matrix with each row corresponding to the nadir point
+  # of a single set. We hence apply the FUN rowwise again.
+  point = apply(sapply(sets2, function(set) {
+    apply(set, 1L, FUN)
+  }), 1L, FUN)
+
+  return(point)
+}
+
+
+# Helper function to check if all given sets have the same dimension, i.e.,
+# number of objectives.
+#
+# @param x [list]
+#   List of sets, i.e., matrizes.
+# @return Nothing
+assertListOfPointSets = function(x) {
+  assertList(x, types = "matrix")
+  n.rows = sapply(x, nrow)
+  if (length(unique(n.rows)) > 1L) {
+    stopf("All sets need to be of the same dimension.")
+  }
+}

man/reference_point_approximation.Rd

@@ -0,0 +1,27 @@
+% Generated by roxygen2 (4.1.1): do not edit by hand
+% Please edit documentation in R/approximatePoints.R
+\name{approximateNadirPoint}
+\alias{approximateIdealPoint}
+\alias{approximateNadirPoint}
+\title{Reference point approximations.}
+\usage{
+approximateNadirPoint(..., sets = NULL)
+
+approximateIdealPoint(..., sets = NULL)
+}
+\arguments{
+\item{...}{[any]\cr
+Sets as matrizes.}
+
+\item{sets}{[\code{list}]\cr
+List of sets. This is an alternative way of passing the sets. Can be used
+exclusively or combined with \code{...}.}
+}
+\value{
+[numeric] Reference point.
+}
+\description{
+Helper functions to compute nadir or ideal point from sets of points, e.g.,
+multiple approxiamtion sets.
+}
+