在列表中获得所有可能的组合

Question

假设我有这样的事情:

L1=['cat', 'dog', 'fish', 'rabbit', 'horse', 'bird', 'frog', 'mouse'...]

for x in L1:
    input1= open('file_%s'%(x), 'r')
    file1= pickle.load(input1)
    for x in L1:
        input2= open('file_%s'%(x), 'r')
        file2= pickle.load(input2)

我希望获得文件的每个组合而不重复已经完成的组合(一旦完成cat_dog,就不要再执行dog_cat).有没有办法可以做到这一点？我的真实列表按字母顺序排列,如果这有任何区别的话.

Answer 1

实际上,你要问的是如何做出名单列表中所有两个项目的组合(而不是所有可能的组合).

这意味着您可以使用内置itertools.combinations()生成器函数轻松(并且有效地)生成所需的名称对,而无需重复:

L1 = ['cat', 'dog', 'fish', 'rabbit', 'horse', 'bird', 'frog', 'mouse']

for pair in combinations(L1, 2):
    print(pair)
    input1 = open('file_%s' % pair[0], 'r')
    input2 = open('file_%s' % pair[1], 'r')

成对的对:

('cat', 'dog')
('cat', 'fish')
('cat', 'rabbit')
('cat', 'horse')
('cat', 'bird')
('cat', 'frog')
('cat', 'mouse')
('dog', 'fish')
('dog', 'rabbit')
('dog', 'horse')
('dog', 'bird')
('dog', 'frog')
('dog', 'mouse')
('fish', 'rabbit')
('fish', 'horse')
('fish', 'bird')
('fish', 'frog')
('fish', 'mouse')
('rabbit', 'horse')
('rabbit', 'bird')
('rabbit', 'frog')
('rabbit', 'mouse')
('horse', 'bird')
('horse', 'frog')
('horse', 'mouse')
('bird', 'frog')
('bird', 'mouse')
('frog', 'mouse')

Answer 2

itertools.combinations怎么样？

用法示例:

>>> list(itertools.combinations([1, 2, 3, 4, 5, 6], 2))
[(1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (2, 3), (2, 4), (2, 5), (2, 6), (3, 4),
(3, 5), (3, 6), (4, 5), (4, 6), (5, 6)]

第一个参数是可迭代的,第二个是r返回的子序列的长度.

然后,您可以使用地图或理解轻松地连接结果:

map(lambda x: x[0] + "_" + x[1], itertools.combinations(["cat", "dog", "fish"], 2)))

x在lambda中是一个r大小的元组.

上述结果将是:

['cat_dog', 'cat_fish', 'dog_fish']

Answer 3

你也可以做它作为一个发电机:

L1=['cat', 'dog', 'fish', 'rabbit', 'horse', 'bird', 'frog', 'mouse']
tuples = [(x,y) for x in L1 for y in L1 if x != y]
for entry in tuples:
    if (entry[1], entry[0]) in tuples:
        tuples.remove((entry[1],entry[0]))
for pair in tuples:
    input1= open('file_%s'%(pair[0]), 'r')
    file1= pickle.load(input1)
    input2= open('file_%s'%(pair[1]), 'r')
    file2= pickle.load(input2)

在第一个循环之后,内容tuples是:

('cat', 'dog')
('cat', 'fish')
('cat', 'rabbit')
('cat', 'horse')
('cat', 'bird')
('cat', 'frog')
('cat', 'mouse')
('dog', 'fish')
('dog', 'rabbit')
('dog', 'horse')
('dog', 'bird')
('dog', 'frog')
('dog', 'mouse')
('fish', 'rabbit')
('fish', 'horse')
('fish', 'bird')
('fish', 'frog')
('fish', 'mouse')
('rabbit', 'horse')
('rabbit', 'bird')
('rabbit', 'frog')
('rabbit', 'mouse')
('horse', 'bird')
('horse', 'frog')
('horse', 'mouse')
('bird', 'frog')
('bird', 'mouse')
('frog', 'mouse')