How to remove duplicate elements from a list in Python

Delete by traversing the list directly

l1 = [1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]

for el in l1:
    if l1.count(el) > 1:
        l1.remove(el)
print(l1)# 会漏删,因为删除一个元素后,后面的元素向前补位,导致紧跟的一个元素被跳过.

Delete by traversing the index

l1 = [1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
for el in range(len(l1)):  # 此时len(l1)已经确定,不会随着l1后面的变化而变化
    if l1.count(l1[el]) > 1:
        l1.remove(l1[el])
print(l1)  # 会报错,因为删除元素后导致l1的长度变短了,但是for遍历的还是之前的索引长度,会导致索引超过范围而报错

Delete the original list by traversing the created slice

l1 = [1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
for el in l1[:]:
    if l1.count(el) > 1:
        l1.remove(el) # 没有问题,可以去重,但是无法保留原有的顺序
print(l1)

Use the new list Record the elements that need to be retained

l1 = [1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
lst = []
for el in l1:
    if lst.count(el) < 1:
        lst.append(el)
print(lst)   # 没有问题,也能保留原有顺序,但是创建了新列表

Delete through index backwards

l1 = [1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
for el in range(len(l1)-1, -1, -1):
    if l1.count(l1[el]) > 1:
        l1.pop(el)  # 没有问题,且保留原顺序
        # l1.remove(l1[el]) # 没有问题,但是不能保留原有顺序
        # del l1[el] # 这样则会保留原有顺序,小伙伴可以想一想为什么
print(l1)

Delete through recursive function

l1 = [1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
def set_lst(lst):
    for el in lst:
        if lst.count(el) > 1:
            lst.remove(el)
            set_lst(lst)    # 每次开辟一个新函数,判断上次被删除了一个元素后的列表
    else:  # 直到最后,列表里的元素都是一个,运行了else
        return lst
print(set_lst(l1))  # 因为是从前面开始删除的,所以不保留原有顺序
'''
[1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
[1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
[1, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
[1, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
[1, 3, 3, 3, 6, 6, 5, 5, 2, 2]
[1, 3, 3, 6, 6, 5, 5, 2, 2]
[1, 3, 6, 6, 5, 5, 2, 2]
[1, 3, 6, 5, 5, 2, 2]
[1, 3, 6, 5, 2, 2]
[1, 3, 6, 5, 2]   return lst = [1, 3, 6, 5, 2]
'''

There is no doubt that set() is the most convenient

l1 = [1, 1, 2, 2, 3, 3, 3, 3, 6, 6, 5, 5, 2, 2]
lst = list(set(l1))
print(lst)

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