如何保留可变长度

Question

我有兴趣在 Python 中使用 DEAP 应用遗传算法。 knapasack can be seen here 的示例实现。我正在尝试创建自己的交叉函数，我想保留 parents 的长度，如下所示：

# Crossover
def crossover(ind1, ind2):
    print len(ind1), len(ind2) #<------ length at the beginning
    temp1 = copy.deepcopy(set(ind1))
    temp2 = copy.deepcopy(set(ind2))
    uniform = list(temp1.union(temp2))
    while len(ind1) > 0:
        ind1.pop()
    while len(ind2) > 0:
        ind2.pop()
    for i in range(max_no):
        ind1.add(random.choice(uniform))
        ind2.add(random.choice(uniform))
    print len(ind1), len(ind2) #<---- length at the end
    return ind1, ind2

但是，函数开头的ind1和in2的长度与结尾的ind1和ind2的长度不同。开头的ind1和ind2的长度应该等于max_no。我希望有人能给我一个提示，说明为什么会这样。我很困惑。

谢谢，如有任何帮助，我们将不胜感激。

编辑：这是我的突变函数。如您所见，我也试图在此处保留个体的可变长度

def mutation(individual):
    if len(individual) > 0:
        individual.remove(random.choice(list(individual)))
        individual.add(random.choice(nodes))
    return individual,

Answer 1

您的代码大致等同于：

import random

ind1 = set(range(100))
ind2 = set(range(100)[::-1])
uniform = list(ind1.union(ind2))
max_no = 100
while len(ind1) > 0:
        ind1.pop()
while len(ind2) > 0:
    ind2.pop()
for i in range(max_no):
    ind1.add(random.choice(uniform))
    ind2.add(random.choice(uniform))

结果

>>> print(len(ind1),len(ind2))
(64, 61)

因为你的个体是集合，所以当你添加随机数时，每隔一段时间就会发生添加两次的情况。然后结果集的长度在每个运行上都会不同，因为如果它已经在个人中，则不会添加任何内容。

要解决您的问题，您可以使用 random.sample 代替：

import random

ind1 = set(range(100))
ind2 = set(range(-100,0,-1)[::-1])
uniform = list(ind1.union(ind2))
max_no = 100
while len(ind1) > 0:
    ind1.pop()
while len(ind2) > 0:
    ind2.pop()
for x in random.sample(uniform,max_no):
    ind1.add(x)
for x in random.sample(uniform,max_no):
    ind2.add(x)

结果

>>> print(len(ind1),len(ind2))
(100, 100)

话虽如此，set 个人对我来说非常痛苦。 sequence 个人是迄今为止得到最好支持的。来自 documentation it's apparent that dict and set as a special case of dict are not considered sequence types:

sequence

An iterable which supports efficient element access using integer indices via the getitem() special method and defines a len() method that returns the length of the sequence. Some built-in sequence types are list, str, tuple, and bytes. Note that dict also supports getitem() and len(), but is considered a mapping rather than a sequence because the lookups use arbitrary immutable keys rather than integers.

如何保留可变长度

How to preserve variable length

python

algorithm

genetic

deap

结果

结果