public async Task <ImmutableHashSet <TChromosome> > SelectAsync(
IEnumerable <TChromosome> parents,
IEnumerable <TChromosome> offspring,
int expectedOffspringCount,
CancellationToken token)
{
var uniqueOffspring = offspring.ToImmutableHashSet();
if (uniqueOffspring.Count <= expectedOffspringCount)
{
return(uniqueOffspring);
}
var fronts = FastNondominatedSorter
.Sort(uniqueOffspring, _offspringComparer);
var selectedOffspring = new List <TChromosome>();
IEnumerable <TChromosome> lastFront = new TChromosome[] { };
foreach (var front in fronts)
{
if (selectedOffspring.Count + front.Count() > expectedOffspringCount)
{
lastFront = front;
break;
}
selectedOffspring.AddRange(front);
}
if (selectedOffspring.Count >= expectedOffspringCount)
{
return(selectedOffspring
.Take(expectedOffspringCount)
.ToImmutableHashSet());
}
return(await _selector.SelectAsync(
selectedOffspring.ToImmutableHashSet(),
lastFront.ToImmutableHashSet(),
expectedOffspringCount, token));
}
public async Task <ImmutableHashSet <TChromosome> > SelectAsync(
IEnumerable <TChromosome> parents,
IEnumerable <TChromosome> offspring,
int expectedOffspringCount,
CancellationToken token)
{
var uniqueOffspring = offspring.ToImmutableHashSet();
if (uniqueOffspring.Count <= expectedOffspringCount)
{
return(uniqueOffspring);
}
var fronts = FastNondominatedSorter.Sort(uniqueOffspring, _offspringComparer);
var selectedOffspring = new List <TChromosome>();
IEnumerable <TChromosome> lastFront = new TChromosome[] { };
foreach (var front in fronts)
{
if (selectedOffspring.Count + front.Count() > expectedOffspringCount)
{
lastFront = front;
break;
}
selectedOffspring.AddRange(front);
}
if (selectedOffspring.Count >= expectedOffspringCount)
{
return(selectedOffspring.Take(expectedOffspringCount).ToImmutableHashSet());
}
var calculatable = lastFront.Union(selectedOffspring).ToArray();
var tasks = _objectives.Select(async objective =>
{
double CalculateDistance(TChromosome left, TChromosome right)
{
return(Math.Sqrt(_objectives.Sum(innerObjective =>
Math.Pow(_mapper.GetValue(innerObjective, left.Fitness) -
_mapper.GetValue(innerObjective, right.Fitness), 2))));
}
var orderedChromosome = calculatable.OrderBy(chromosome =>
_mapper.GetValue(objective, chromosome.Fitness))
.ThenBy(chromosome =>
_objectives.Average(obj => _mapper.GetValue(obj, chromosome.Fitness)))
.ToImmutableArray();
var first = orderedChromosome.First();
var last = orderedChromosome.Last();
var distances = calculatable.ToDictionary(chromosome => chromosome, _ => 0d);
var longestDistance = CalculateDistance(first, last);
distances[first] += longestDistance;
distances[last] += longestDistance;
var innerTasks = orderedChromosome.Skip(1).Take(orderedChromosome.Length - 2)
.Select((chromosome, i) => Task.Run(() =>
{
var upper = orderedChromosome[i + 2];
var lower = orderedChromosome[i];
distances[chromosome] += CalculateDistance(upper, lower);
}, token));
await Task.WhenAll(innerTasks);
return(distances);
});
var allDistances = await Task.WhenAll(tasks);
return(calculatable.ToDictionary(chromosome => chromosome, chromosome =>
allDistances.Sum(distances => distances[chromosome]))
.OrderByDescending(kv => kv.Value)
.Take(expectedOffspringCount)
.Select(kv => kv.Key)
.ToImmutableHashSet());
}
