/// <summary>
/// Try few times to find an unused pair (unless avoidPairRepetition
/// is false.
/// </summary>
protected override IEnumerable <IGenome> PerformSelection(int nbToSelect)
{
var result = new IGenome[nbToSelect];
for (int tries = 0; tries < nbOfTriesToAvoidRepetition; tries++)
{
// Remove the best genomes depending on the number of tries.
if (tries != 0 && tries % removeBestIfExceedsTriesCap == 0)
{
var best = genomeAndFitn.MaxBy(x => x.Value).Key;
genomeAndFitn.Remove(best);
}
// Use a copy of the dictionary so that the sets don't have
// repeating genomes.
var genomeAndFitnCpy = genomeAndFitn.ToDictionary(
x => x.Key,
x => x.Value);
var fitness = genomeAndFitnCpy.Sum(x => x.Value);
for (int i = 0; i < nbToSelect; i++)
{
var targetFitness = GARandomManager.NextFloat(0, fitness);
IGenome target = null;
foreach (var pair in genomeAndFitnCpy)
{
if (targetFitness <= pair.Value)
{
target = pair.Key;
break;
}
else
{
targetFitness -= pair.Value;
}
}
Debug.Assert(target != null);
fitness -= genomeAndFitnCpy[target];
genomeAndFitnCpy.Remove(target);
result[i] = target;
}
if (!avoidPairRepetition)
{
return(result);
}
// Order the set, to make it work for cases like:
// (1, 5, 2) and (2, 1, 5).
result = result.OrderBy(x => x.Fitness).ToArray();
if (!SetOfGenomesAlreadyUsed(result))
{
usedSetsOfGenomes.Add(result);
return(result);
}
}
throw new Exception("Too many tries for a selection.");
}