Tournament Selection Average Fitness not increasing?

Question

I am trying to implement a genetic tournament selection algorithm, where the fitness of the population on average goes up, but my average fitness isn't changing.

I would appreciate if anyone could take a look at my code and advise me on what I am doing wrong. You can find the code here: https://github.com/Mithycal/tournament-selection-algorithm

Code for finding fitness:

for i in range(len(individuals)):
            chosen = individuals[i]
            fitness_scores.append(sum(([a * b for a, b in zip(equation_inputs, chosen)])))

Answer 1

i have taken a look into your code. In this point, tournamentSize is the size of each group right?

for k in range(tournamentSize):
    randchoice = random.sample(list(individuals), 1)[0] #update individual list so values are different??!
    randvalue = individuals.get(randchoice)
    random_individuals.append(randvalue)
    loc = list(individuals).index(randchoice)
    random_fitness_scores.append(fitness_scores[loc])
    print("\n", randchoice, "participates in the tournament")
print("\n")

If i remember right in this selection you want to divide your poblation into N groups of individuals, and then you want to keep only the best ( or the n best) of each group.

I recomend you to change the population representation to:

individuals = [[random.randint(-4,4) for _ in range(number_of_genes)] for i in pop ] # list

So you could do something like: score() -> custom function that retuns the fitness of an individual

choosen_individuals = []
#go throw individual jumping tournamentSize each time
for k in range(0,len(individuals),tournamentSize): 
    tournament_individuals = individuals[k:k+tournamentSize] # current group
    sorted_group = sorted( [ (score(individual),index) for index,individual in enumerate(tournament_individuals)],reverse = True)
    #sorted_group contains a list of tuples (score,individual_position)
    choosen_individuals.append(tournament_individuals[sorted_group[1]]) # saves the best

I'm leaving you one genetic that i implemented: https://github.com/anigmo97/MUIARFID/blob/master/CUATRIMESTRE_1A/TIA/PROYECTO/algoritmo_gen%C3%A9tico/geneticos.py

I hope it helps.

YOUR IMPLEMENTATION

INDIVIDUAL REPRESENTATION

Now your individuals (rename to population) are a list of gens. your population is a dict with key (int) and value list of ints. If you think about it, basically you are using the dict as it was a list. I recommend you to change the representation of a population from something like:

{0 : [ 2,-3], 1: [-1,-1]}

TO

[[2,-3],[-1,-1]]

CHANGING

individuals = { i : [random.randint(-4,4) for _ in range(number_of_genes)] for i in pop }

population = []
for i in range(population_size):
    population.append([random.randint(-4,4) for _ in range(number_of_genes)])

INDIVIDUAL SCORING

You have a list of weights for each gen so we have a list called "weights" with length = number_of_genes. (The individual has the same length).

With the new representation your scoring can be like:

def score_individual(individual):
    return sum(([a * b for a, b in zip(weights, individual)]))

def fitness_calc(population):
    fitness_scores = [] #local variable
    for individual in population:
        chosen = list(individuals.values())[i]
        fitness_scores.append(score_individual(individual)) 
    return fitness_scores

POPULATION SORTING

def sort_population_by_fitness(population):
     return sorted(population,key=lambda i:score_individual(i),reverse=True)

COMPLETE EXAMPLE

from random import randint,shuffle

def generate_random_weights(num_weights):
    return [randint(-200,200) for x in range(num_weights)]


def generate_population(number_of_gens):
    population = []
    for i in range(population_size):
        population.append([randint(-4, 4) for _ in range(number_of_gens)])
    return population

def score_individual(individual):
    return sum(([a * b for a, b in zip(weights, individual)]))

def fitness_calc(population):
    fitness_scores = [] #local variable
    for individual in population:
        fitness_scores.append(score_individual(individual))
    return fitness_scores

def sort_population_by_fitness(population):
    return sorted(population,key=lambda i:score_individual(i),reverse=True)

def calculate_population_score_avg(population):
    scores = [score_individual(i) for i in population]
    return sum(scores)/len(scores)

def make_tournament_selection(population,group_size):
    shuffle(population)
    choosen_individuals = []
    #go throw individual jumping tournamentSize each time
    for k in range(0, len(population), group_size):
        tournament_individuals = population[k:k + group_size]  # current group
        sorted_group = sort_population_by_fitness(tournament_individuals)
        choosen_individuals.append(sorted_group[0])
        print("---->BEST INDIVIDUAL OF THE GROUP {}".format(score_individual(sorted_group[0])))
    return choosen_individuals

def make_n_best_selection(population,num_individuals_to_keep):
    return sort_population_by_fitness(population)[:num_individuals_to_keep]



if __name__ =="__main__":
    population_size = 20
    number_of_gens = 10
    weights = generate_random_weights(number_of_gens)
    population = generate_population(number_of_gens)

    num_generations = 10
    group_size = 5
    score_avgs_by_generation = []
    for i in range(num_generations):
        # make selection
        #population = make_tournament_selection(population,group_size)
        population = make_n_best_selection(population,5)
        print("BEST SCORE IN GENERATION {} = {}".format(
            i,score_individual(sort_population_by_fitness(population)[0]))
        )
        avg_score = calculate_population_score_avg(population)
        score_avgs_by_generation.append(avg_score)
        print("SCORE AVG  IN GENERATION {} = {}\n\n".format(i, avg_score))

        # make crossbreeding
        # make mutations
        # add random individuals to add new genetic load
        population += generate_population(10)