[英]python combination of k size from n size list (recursive)
我需要一个递归函数,该函数可以对给定的列表和长度进行所有可能的置换,并进行替换:
>>> rec_offspring(3,[2,3])
[[2, 2, 2], [3, 2, 2], [2, 3, 2], [3, 3, 2], [2, 2, 3], [3, 2, 3], [2, 3, 3], [3, 3, 3]]
我在下面找到了代码,但只给出了连击; 它不会重复元素,例如[222] [322]等。
def choose_sets(mylist,length):
mylen = len(mylist)
if length == 1:
return [[i] for i in mylist]
if length > mylen:
return []
ToRet = []
for k in xrange(mylen):
if mylen - k + 1> length :
for j in choose_sets(mylist[k+1:],length-1):
New = [mylist[k]]
New.extend(j)
ToRet.append(New)
return ToRet
print choose_sets([1,2,3,4,5],3)
这称为笛卡尔积。 您可以使用itertools
模块 :
>>> from itertools import product
>>> list(product([2,3], repeat=3))
[(2, 2, 2), (2, 2, 3), (2, 3, 2), (2, 3, 3), (3, 2, 2), (3, 2, 3), (3, 3, 2), (3, 3, 3)]
您有三个基本问题:
(1)在递归调用中,您砍掉了所选元素。 而是将它们全部传递到下一个级别。 更换
for j in choose_sets(mylist[k+1:],length-1):
与
for j in choose_sets(mylist,length-1):
(2)您限制了要考虑的元素的数量,以使这些元素按非降序排列。 删除线
if mylen - k + 1> length:
(3)最后,将返回列表限制为输入列表的长度。 这意味着只有2个元素(例如[2,3])不能返回3个元素(例如[2,3,2])的选择列表。 删除有问题的代码:
if length > mylen:
return []
结果程序看起来像您想要的,返回:
>>> print choose_sets([2,3], 3)
[[2, 2, 2], [2, 2, 3], [2, 3, 2], [2, 3, 3], [3, 2, 2], [3, 2, 3], [3, 3, 2], [3, 3, 3]]
>>> print choose_sets([1,2,3,4,5], 3)
[[1, 1, 1], [1, 1, 2], [1, 1, 3], [1, 1, 4], [1, 1, 5], [1, 2, 1], [1, 2, 2], [1, 2, 3], [1, 2, 4], [1, 2, 5], [1, 3, 1], [1, 3, 2], [1, 3, 3], [1, 3, 4], [1, 3, 5], [1, 4, 1], [1, 4, 2], [1, 4, 3], [1, 4, 4], [1, 4, 5], [1, 5, 1], [1, 5, 2], [1, 5, 3], [1, 5, 4], [1, 5, 5], [2, 1, 1], [2, 1, 2], [2, 1, 3], [2, 1, 4], [2, 1, 5], [2, 2, 1], [2, 2, 2], [2, 2, 3], [2, 2, 4], [2, 2, 5], [2, 3, 1], [2, 3, 2], [2, 3, 3], [2, 3, 4], [2, 3, 5], [2, 4, 1], [2, 4, 2], [2, 4, 3], [2, 4, 4], [2, 4, 5], [2, 5, 1], [2, 5, 2], [2, 5, 3], [2, 5, 4], [2, 5, 5], [3, 1, 1], [3, 1, 2], [3, 1, 3], [3, 1, 4], [3, 1, 5], [3, 2, 1], [3, 2, 2], [3, 2, 3], [3, 2, 4], [3, 2, 5], [3, 3, 1], [3, 3, 2], [3, 3, 3], [3, 3, 4], [3, 3, 5], [3, 4, 1], [3, 4, 2], [3, 4, 3], [3, 4, 4], [3, 4, 5], [3, 5, 1], [3, 5, 2], [3, 5, 3], [3, 5, 4], [3, 5, 5], [4, 1, 1], [4, 1, 2], [4, 1, 3], [4, 1, 4], [4, 1, 5], [4, 2, 1], [4, 2, 2], [4, 2, 3], [4, 2, 4], [4, 2, 5], [4, 3, 1], [4, 3, 2], [4, 3, 3], [4, 3, 4], [4, 3, 5], [4, 4, 1], [4, 4, 2], [4, 4, 3], [4, 4, 4], [4, 4, 5], [4, 5, 1], [4, 5, 2], [4, 5, 3], [4, 5, 4], [4, 5, 5], [5, 1, 1], [5, 1, 2], [5, 1, 3], [5, 1, 4], [5, 1, 5], [5, 2, 1], [5, 2, 2], [5, 2, 3], [5, 2, 4], [5, 2, 5], [5, 3, 1], [5, 3, 2], [5, 3, 3], [5, 3, 4], [5, 3, 5], [5, 4, 1], [5, 4, 2], [5, 4, 3], [5, 4, 4], [5, 4, 5], [5, 5, 1], [5, 5, 2], [5, 5, 3], [5, 5, 4], [5, 5, 5]]
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