python列表中的不同值

Question

I need to extract unique values in python list by omitting the repeated values altogether:

Input:

lis = ['a','l','f','a']

Desired Output:

lis2 = ['l','f']

So I need to remove all duplicate iteams. Sets won't do cause I don't want 'a' in it

Answer 1

You basically want items which count in the list is only 1. Count of items in the list - use Counter class

from collections import Counter
lis = ['a','l','f','a']
counter = Counter(lis)
lis2 = [elem for elem in lis if counter[elem] == 1]
print(lis2)

You could also use list.count , but that would go through the list each time, giving you O(n^2) complexity, while creating the Counter is O(n) and then checking count is O(1) (n times), resulting in O(n) .

Answer 2

this little function will create a dictionary of the number of occurrences of each element, then filter out the ones with multiple occurrences, and return the resulting list.

lst = ['a','b', 'c', 'a']

def removeDupes(lst):
    counts = {}
    for item in lst:
        if counts.get(item):
            counts[item] += 1
        else:
            counts[item] = 1
    result = dict({(k, v) for k, v in counts.items() if v == 1})
    return result.keys()

print(removeDupes(lst)) # outputs: ['b', 'c']

Answer 3

这是一个简单的衬垫！

lis2 = list(set(lis) - set([x for x in lis if lis.count(x) > 1]))