# Roulette wheel

mattia gervaz at gmail.com
Wed Mar 4 19:02:05 CET 2009

```Hi everyone, I'm new to python and I want to create some simple code in
order to code the classical genetic algorithm example: given a population
of chromosomes, encoded using 1 and 0, find the chromosome with the
maximum number of 1s. Now, despite all the code used to implement the
solution, I'm wondering if there is a better way to use the so-called
roulette wheel selection in this problem. Here I paste the code of my

from random import randint, random

def create_chromosome(min, max, length):
chromosome = []
for i in range(length):
chromosome.append(randint(min, max))
return chromosome

def fitness(chrm, ffunc=sum):
return ffunc(chrm)

def create_population(nelem, min, max, length):
return [create_chromosome(min, max, length) for i in range(nelem)]

def get_fitness_and_population(population):
return [(fitness(x), x) for x in population]

def get_roulette_wheel(population):
roulette_wheel = []
index = 0

for x in get_fitness_and_population(population):
for j in range(x[0]):
roulette_wheel.append(index)
index += 1

return roulette_wheel

pop = create_population(5, 0, 1, 10)
rw = get_roulette_wheel(pop)
print(rw)
print(len(rw))
ri = randint(0, len(rw) - 1)
print("Random index:", rw[ri], ", value:", pop[rw[ri]])

```