/// <summary>
/// order-based crossover operator (OX2)
/// Precondition: parent1 and parent2 contain the same alleles.
/// Postcondition: child contains the same alleles as parent1.
/// </summary>
/// <param name="parent1"></param>
/// <param name="parent2"></param>
/// <returns></returns>
public Genotype OrderBasedCrossover(Genotype parent1, Genotype parent2)
{
var count = parent1.Count;
if (count <= 1)
{
return(parent1);
}
var minNumberOfPositions = (int)Math.Max(1, count * MinimumNumberOfPositionsFactor);
var maxNumberOfPositions = (int)Math.Max(1, count * MaximumNumberOfPositionsFactor);
var numberOfPositions = random.Next(minNumberOfPositions, maxNumberOfPositions);
// select alleles
var selectedAllelesP2 = new HashSet <int>();
for (int i = 0; i < numberOfPositions; i++)
{
if (!selectedAllelesP2.Add(parent2[random.Next(0, count)]))
{
// already selected, try again
i--;
}
}
// copy alleles from parent1 which are not selected
var emptyIndices = new List <int>(count - numberOfPositions);
var child = new int[count];
for (int i = 0; i < count; i++)
{
var allele = parent1[i];
if (!selectedAllelesP2.Contains(allele))
{
child[i] = allele;
}
else
{
emptyIndices.Add(i);
}
}
// add the missing alleles in the order they appear in parent2
var nextPositionParent2 = 0;
var missingAlleles = parent2.Intersect(selectedAllelesP2).ToArray();
foreach (var i in emptyIndices)
{
// find next allele
child[i] = missingAlleles[nextPositionParent2];
nextPositionParent2++;
}
return(new Genotype(child));
}