def mutate(self, pruning=False):
"""
Alter a random node in chromosomes.
"""
# randomly select node to mutate
mpoint = r.randint(0, self.size - 1)
# mutate whole node by replacing children with random subtree
if r.random() >= 0.5:
rand_tree = random_tree(2)
x2 = r.randint(0, rand_tree.node_num - 1)
node = rand_tree.get_node(x2)
self.chromosomes.set_node(mpoint, node)
# check and prune tree with new subtree for inefficiencies
if pruning:
self.chromosomes.prune()
# or just mutate node value based on current type
else:
node = self.chromosomes.get_node(mpoint)
# constant
if node.value in CONSTS:
mutated_value = CONSTS[r.randint(0, len(CONSTS) - 1)]
# variable
elif node.value in eugene.Config.VAR.keys():
mutated_value = eugene.Config.VAR.keys()[r.randint(0, len(eugene.Config.VAR.keys()) - 1)]
# a unary operator
elif node.value in UNARIES:
mutated_value = UNARIES[r.randint(0, len(UNARIES) - 1)]
# a binary operator
elif node.value in BINARIES:
mutated_value = BINARIES[r.randint(0, len(BINARIES) - 1)]
# a n-ary operator
# elif node.value in NARIES:
# mutated_value = NARIES[r.randint(0, len(NARIES) - 1)]
# EPHEMERAL constant random ( 0:1, uniform -500:500, or normal -500:500 )
else:
mutated_value = EPHEMERAL[r.randint(1, len(EPHEMERAL) - 1)]()
# mutate node value (keeps children, if applicable)
node.value = mutated_value
self.chromosomes.set_node(mpoint, node)
def test_12_random_trees(self):
"""Generate 500 random trees"""
NUM_TREES = 500
random_trees = [random_tree(10) for i in xrange(NUM_TREES)]
self.assertEqual(len(random_trees), NUM_TREES)
