R/operator.EARecombinatorOX.R

In jakobbossek/ecr3: Evolutionary Computation in R - Version 3

#' @title
#' Ordered-Crossover (OX) recombinator.
#'
#' @description
#' This recombination operator is specifically designed for permutations.
#' The operators chooses two cut-points at random and generates two offspring
#' as follows: a) copy the subsequence of one parent and b) remove the copied
#' node indizes from the entire sequence of the second parent from the sescond
#' cut point and b) fill the remaining gaps with this trimmed sequence.
#'
#' @param inds [\code{list}]\cr
#'   Parents, i.e., list of exactly two permutations (vectors of integer values) of equal length.
#' @return [\code{list}]
#' @family recombinators
#' @export
EARecombinatorOX = function() {
  EARecombinator$new(
    name = "OX recombination",
    representations = "permutation",
    params = list(),
    n.parents = 2L,
    n.children = 2L,
    fun = function(inds) {
      p1 = inds[[1L]]
      p2 = inds[[2L]]
      n = length(p1)

      # select two random positions and bring them in order
      idx = sample(1:(n - 1), 2L)
      cut1 = idx[1L]
      cut2 = idx[2L]
      if (cut2 < cut1) {
        tmp = cut1
        cut1 = cut2
        cut2 = tmp
      }

      # length of copied subsequence
      m = cut2 - cut1 + 1L

      # number of missing elements
      n.miss = length(p1) - m - 1L

      # copy the subsequence
      c1 = rep(NA, n)
      c2 = rep(NA, n)

      # copy subsequences
      c1[cut1:cut2] = p1[cut1:cut2]
      c2[cut1:cut2] = p2[cut1:cut2]

      # now take "the rest" from the other parent from the second cut points ...
      r1 = p2[(((cut2):(cut2 + n)) %% n) + 1L]
      r2 = p1[(((cut2):(cut2 + n)) %% n) + 1L]

      # ... and remove the already copied stuff
      r1 = setdiff(r1, p1[which(!is.na(c1))])
      r2 = setdiff(r2, p2[which(!is.na(c2))])

      # complete the child sequences
      c1[(cut2:(cut2 + n.miss) %% n) + 1L] = r1
      c2[(cut2:(cut2 + n.miss) %% n) + 1L] = r2

      return(list(c1, c2))
    }
  )
} # EARecombinatorOX