public static Chromosome[] rouletteSelect(Chromosome[] population, int numToSelect)
{
Chromosome[] toReturn = new Chromosome[numToSelect];
int[] popIndex = new int[population.Length];
bool[] hasBeenSelected = new bool[population.Length];
// sort and compute total fitness
int fitnessSum = 0;
population = population.OrderByDescending(x => x.getFitnessScore()).ToArray();
int previousFitness = 0;
int counter = 0;
foreach (Chromosome chrome in population)
{
popIndex[counter] = chrome.getFitnessScore() + previousFitness;
previousFitness = popIndex[counter];
counter++;
fitnessSum += chrome.getFitnessScore();
}
int selected;
for(int i = 0; i < numToSelect; i++)
{
selected = Program.rng.Next(fitnessSum);
int index = 0;
while (selected >= popIndex[index])
{
index++;
}
// chrome @ current index was selected from the roulette
// if the chromosome has already been selected, we just randomly
// generate another number. This is an easy way to do this but
// can potentially take a long time to finish the selection if
// the proportion of selected to not selected is high.
if (!hasBeenSelected[index])
{
toReturn[i] = population[index];
hasBeenSelected[index] = true;
}
else
{
// we don't want to go to the next index since we tried
// to select something already selected
i--;
}
}
return toReturn;
}
