Question

所以我现在正在参加一个计算机科学入门课程，我想知道如何检查多个列表中是否有任何重复项目。我已经阅读了这些答案：

How can I compare two lists in python and return matches和How to find common elements in list of lists?

但是，它们并不是我想要的。比方说我有这个列表列表：

list_x = [[66,76], 
          [25,26,27], 
          [65,66,67,68], 
          [40,41,42,43,44], 
          [11,21,31,41,51,61]]

有两套重复（66和41），虽然这对我来说并不重要。有没有办法找出是否存在重复项？我正在寻找的是，如果有重复，该函数将返回True（或False，取决于我想对列表做什么）。我得到的印象是我应该使用集合（我们没有学到这些，所以我在互联网上查找），使用循环或编写我自己的函数。如果我需要编写自己的函数，请告诉我，我将在今天晚些时候进行编辑！

Answer 1

一个非常简单的解决方案是使用list comprehension首先展平列表，然后一起使用set和len来测试任何重复项：

>>> list_x = [[66,76],
...           [25,26,27],
...           [65,66,67,68],
...           [40,41,42,43,44],
...           [11,21,31,41,51,61]]
>>> flat = [y for x in list_x for y in x]
>>> flat # Just to demonstrate
[66, 76, 25, 26, 27, 65, 66, 67, 68, 40, 41, 42, 43, 44, 11, 21, 31, 41, 51, 61]
>>> len(flat) != len(set(flat)) # True because there are duplicates
True
>>>
>>> # This list has no duplicates...
... list_x = [[1, 2],
...           [3, 4, 5],
...           [6, 7, 8, 9],
...           [10, 11, 12, 13],
...           [14, 15, 16, 17, 18]]
>>> flat = [y for x in list_x for y in x]
>>> len(flat) != len(set(flat)) # ...so this is False
False
>>>

但请注意，如果list_x很大，这种方法会有些慢。如果需要考虑性能，那么您可以使用利用generator expression，any和set.add的惰性方法：

>>> list_x = [[66,76],
...           [25,26,27],
...           [65,66,67,68],
...           [40,41,42,43,44],
...           [11,21,31,41,51,61]]
>>> seen = set()
>>> any(y in seen or seen.add(y) for x in list_x for y in x)
True
>>>

Answer 2

迭代并使用一个集来检测是否存在重复：

seen = set()
dupes = [i for lst in list_x for i in lst if i in seen or seen.add(i)]

这利用了seen.add()返回None的事实。 set是一组无序的唯一值;如果i in seen已经是该集合的一部分，则True测试为i。

演示：

>>> list_x = [[66,76], 
...           [25,26,27], 
...           [65,66,67,68], 
...           [40,41,42,43,44], 
...           [11,21,31,41,51,61]]
>>> seen = set()
>>> [i for lst in list_x for i in lst if i in seen or seen.add(i)]
[66, 41]

Answer 3

以下是使用集合的更直接的解决方案：

list_x = [[66,76], 
          [25,26,27], 
          [65,66,67,68], 
          [40,41,42,43,44], 
          [11,21,31,41,51,61]]
seen = set()
duplicated = set()
for lst in list_x:
    numbers = set(lst) # only unique
    # make intersection with seen and add to duplicated:
    duplicated |= numbers & seen 
    # add numbers to seen
    seen |= numbers

print duplicated

有关set及其操作的信息，请参阅文档：https://docs.python.org/2/library/stdtypes.html#set

如何查看列表列表中是否有任何重复项

3 个答案: