swap_mutator.py

from numpy import nan as np_nan
from pygenalgo.genome.chromosome import Chromosome
from pygenalgo.operators.mutation.mutate_operator import MutationOperator


class SwapMutator(MutationOperator):
    """
    Description:

        Swap mutator mutates the chromosome by swapping the gene
        values between two randomly selected gene positions.
    """

    def __init__(self, mutate_probability: float = 0.1):
        """
        Construct a 'SwapMutator' object with a given probability value.

        :param mutate_probability: (float).
        """

        # Call the super constructor with the provided probability value.
        super().__init__(mutate_probability)
    # _end_def_

    def mutate(self, individual: Chromosome) -> None:
        """
        Perform the mutation operation by swapping the genes at two random positions.

        :param individual: (Chromosome).

        :return: None.
        """

        # If the mutation probability is higher than
        # a uniformly random value, make the changes.
        if self.probability > self.rng.random():

            # Select randomly the two mutation points.
            i, j = self.rng.choice(len(individual), size=2, replace=False,
                                   shuffle=False)

            # Swap in place between the two positions.
            individual[i], individual[j] = individual[j], individual[i]

            # Invalidate the fitness of the chromosome.
            individual.fitness = np_nan

            # Increase the mutator counter.
            self.inc_counter()
        # _end_if_
    # _end_def_

# _end_class_