eckity.genetic_operators.crossovers.subtree_crossover

 1from eckity.genetic_operators.genetic_operator import GeneticOperator
 2
 3
 4class SubtreeCrossover(GeneticOperator):
 5    def __init__(self, probability=1, arity=2, events=None):
 6        self.individuals = None
 7        self.applied_individuals = None
 8        super().__init__(probability=probability, arity=arity, events=events)
 9
10    def apply(self, individuals):
11        """
12        Perform subtree crossover between this tree and `other` tree:
13            1. Select random node from `other` tree
14            2. Get subtree rooted at selected node
15            1. Select a random node in this tree
16            2. Place `other` selected subtree at this node, replacing current subtree
17
18        Parameters
19        ----------
20        individuals
21        select_func: callable
22        Selection method used to receive additional individuals to perform crossover on
23
24        individual: Tree
25        tree individual to perform crossover on
26
27        Returns
28        -------
29        a new, modified individual
30        """
31
32        assert len(individuals) == self.arity, f'Expected individuals list of size {self.arity}, got {len(individuals)}'
33
34        self.individuals = individuals
35
36        # select a random subtree from each individual's tree
37        subtrees = [ind.random_subtree() for ind in individuals]
38
39        # assign the next individual's subtree to the current individual's tree
40        for i in range(len(individuals) - 1):
41            individuals[i].replace_subtree(subtrees[i+1])
42
43        # to complete the crossover circle, assign the first subtree to the last individual
44        individuals[-1].replace_subtree(subtrees[0])
45
46        self.applied_individuals = individuals
47        return individuals