Question

我有3个名单：

a = [10, 9, 8, 7, 6]
b = [8, 7, 6, 5, 4, 3]
c = [6, 5, 4, 3, 2]

我需要获得itertools.product()获得的所有排列，但只有在值减少的情况下才能获得：

[10, 8, 6] # is good
[6, 8, 4]  # is not good, since 8 > 6

有一种简单的方法可以做到这一点，还是应该使用列表理解和条件？

Answer 1

你可以通过遍历itertools.product迭代器并仅提取那些反向排序的返回项来实现列表推导：

[item for item in product(a,b,c) if sorted(item, reverse = True) == list(item)]

示例：

from itertools import product
a = [10,9,8,7,6]
b = [8, 7, 6, 5, 4, 3]
c = [6, 5, 4, 3, 2]
[item for item in product(a,b,c) if sorted(item, reverse = True) == list(item)]
# [(10, 8, 6), (10, 8, 5), (10, 8, 4), (10, 8, 3), (10, 8, 2) ...continues

Answer 2

您可以参考以下没有列表推导的代码：

from itertools import product
a = [10, 9, 8, 7, 6]
b = [8, 7, 6, 5, 4, 3]
c = [6, 5, 4, 3, 2]
for result in product(a,b,c):
    if sorted(result, reverse = True) == list(result):
            print result

Answer 3

这是一个简单的单行解决方案

>>> mylist = [10, 9, 8, 7, 6]
>>> all(earlier >= later for earlier, later in zip(mylist, mylist[1:]))
True
>>> mylist = [10, 9, 7, 8, 6]
>>> all(earlier >= later for earlier, later in zip(mylist, mylist[1:]))
False

我在这里找到了这个：

Determine if a list is in descending order

Answer 4

如果您由于某种原因不想使用列表推导：

def decreasing(l):
    return all(a >= b for a, b in zip(l[:-1], l[1:]))


filter(decreasing, product(a, b, c))

产品价值下降

4 个答案: