ryanzidago
Genetic Algorithms in Elixir: Wrong function to calculate the average genes (page 148)
The average_tiger function is written like so in the book:
def average_tiger(population) do
genes = Enum.map(population, & &1.genes)
fitnesses = Enum.map(population, & &1.fitness)
ages = Enum.map(population, & &1.age)
num_tigers = length(population)
avg_fitness = Enum.sum(fitnesses) / num_tigers
avg_age = Enum.sum(ages) / num_tigers
avg_genes =
genes
|> Enum.zip()
|> Enum.map(&(Enum.sum(&1) / num_tigers))
%Chromosome{genes: avg_genes, age: avg_age, fitness: avg_fitness}
end
Genes is a list of list:
[
[1, 1, 1, 0, 1, 1, 0, 1],
[0, 1, 1, 1, 1, 0, 1, 0],
[1, 1, 1, 0, 0, 0, 0, 0],
[0, 0, 1, 1, 1, 1, 0, 0],
[0, 1, 0, 1, 1, 0, 0, 0],
[1, 1, 0, 0, 1, 1, 0, 1],
[0, 1, 0, 1, 0, 0, 0, 1],
[1, 0, 1, 1, 0, 1, 0, 0],
[0, 0, 1, 1, 0, 1, 0, 0],
[0, 1, 0, 0, 1, 0, 0, 1],
[0, 1, 0, 1, 1, 0, 1, 1],
[0, 0, 1, 1, 0, 1, 1, 1],
[0, 0, 1, 1, 0, 0, 1, 1],
[1, 1, 0, 0, 0, 0, 1, 1],
[0, 0, 0, 1, 0, 1, 0, 0],
[0, 0, 0, 1, 1, 0, 0, 0],
[1, 0, 0, 1, 1, 1, 1, 1],
[1, 0, 0, 0, 0, 1, 0, 1],
[1, 0, 0, 1, 1, 0, 1, 1],
[0, 0, 0, 0, 1, 0, 0, 0]
]
With Enum.zip/1 this list of lists is transformed to a list of tuples (with columns zipped together):
[
{1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0},
{1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0},
{1, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0},
{0, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0},
{1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1},
{1, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0},
{0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 0, 1, 0},
{1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0}
]
The problem is that Tuple does not implement the Enumerable protocol so it is not possible to map the element of tuple like this:
genes
|> Enum.zip()
|> Enum.map(&(Enum.sum(&1) / num_tigers))
I think some code got los in the process 
To calculate the average genes, the code should look like this:
avg_genes =
genes
|> Enum.zip()
|> Enum.map(&Tuple.to_list/1)
|> Enum.map(&Enum.sum/1)
|> Enum.map(&(&1 / num_tigers))
|> Enum.map(&Float.round(&1, 2))
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