本文列些處幾種去除在Python 列表中(list)可能存在的重復(fù)項(xiàng),這在很多應(yīng)用程序中都會(huì)遇到的需求,作為程序員最好了解其中的幾種方法 以備在用到時(shí)能夠?qū)懗鲇行У某绦颉?/p>
方法1:樸素方法
這種方式是在遍歷整個(gè)list的基礎(chǔ)上,將第一個(gè)出現(xiàn)的元素添加在新的列表中。
示例代碼:
# Python 3 code to demonstrate
# removing duplicated from list
# using naive methods
# initializing list
test_list = [1, 3, 5, 6, 3, 5, 6, 1]
print ("The original list is : " + str(test_list))
# using naive method
# to remove duplicated
# from list
res = []
for i in test_list:
if i not in res:
res.append(i)
# printing list after removal
print ("The list after removing duplicates : " + str(res))
→ 輸出結(jié)果:
The original list is : [1, 3, 5, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 3, 5, 6]
方法2:列表解析式
這種方式實(shí)際上是第一種方法的簡化版,它利用列表解析式,使用一行代碼就可以替代上面的循環(huán)方式。
示例代碼:
# Python 3 code to demonstrate
# removing duplicated from list
# using list comprehension
# initializing list
test_list = [1, 3, 5, 6, 3, 5, 6, 1]
print ("The original list is : " + str(test_list))
# using list comprehension
# to remove duplicated
# from list
res = []
[res.append(x) for x in test_list if x not in res]
# printing list after removal
print ("The list after removing duplicates : " + str(res))
→ 輸出結(jié)果:
The original list is : [1, 3, 5, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 3, 5, 6]
方法3:使用set()
這種方式是最流行的方法來去除列表中的重復(fù)元素。但該方法的最大的一個(gè)缺點(diǎn)就是使用過后列表中元素的順序不再繼續(xù)保持與原來一致了。
示例代碼:
# Python 3 code to demonstrate
# removing duplicated from list
# using set()
# initializing list
test_list = [1, 5, 3, 6, 3, 5, 6, 1]
print ("The original list is : " + str(test_list))
# using set()
# to remove duplicated
# from list
test_list = list(set(test_list))
# printing list after removal
# distorted ordering
print ("The list after removing duplicates : " + str(test_list))
→ 輸出結(jié)果:
The original list is : [1, 5, 3, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 3, 5, 6]
方法4:利用列表解析式 + enumerate()
該方法是在列表解析式的基礎(chǔ)上利用枚舉來去除重復(fù)元素。通過檢查元素是否已經(jīng)在列表中存在從而將其略過。這種方法可以保持列表中的元素順序不會(huì)改變。
示例代碼:
# Python 3 code to demonstrate
# removing duplicated from list
# using list comprehension + enumerate()
# initializing list
test_list = [1, 5, 3, 6, 3, 5, 6, 1]
print ("The original list is : " + str(test_list))
# using list comprehension + enumerate()
# to remove duplicated
# from list
res = [i for n, i in enumerate(test_list) if i not in test_list[:n]]
# printing list after removal
print ("The list after removing duplicates : " + str(res))
→ 輸出結(jié)果:
The original list is : [1, 5, 3, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 5, 3, 6]
方法5:利用collections.OrderedDict.fromkeys()
這是完成特殊任務(wù)中最快的方法。它先是將列表中的重復(fù)項(xiàng)移除并返回一個(gè)字典,最后轉(zhuǎn)換成列表。這種方法對于字符串也可以進(jìn)行處理。
示例代碼:
# Python 3 code to demonstrate
# removing duplicated from list
# using collections.OrderedDict.fromkeys()
from collections import OrderedDict
# initializing list
test_list = [1, 5, 3, 6, 3, 5, 6, 1]
print ("The original list is : " + str(test_list))
# using collections.OrderedDict.fromkeys()
# to remove duplicated
# from list
res = list(OrderedDict.fromkeys(test_list))
# printing list after removal
print ("The list after removing duplicates : " + str(res))
→ 輸出結(jié)果:
The original list is : [1, 5, 3, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 5, 3, 6]
方法6:處理嵌套列表中的重復(fù)元素
對于多維列表(列表嵌套)中的重復(fù)元素去除。這里假設(shè)列表中元素(也是列表)它們具有相同的元素(但不一定順序相同)都被當(dāng)做重復(fù)元素。那么下面使用 set() + sorted() 方法來完成任務(wù)。
示例代碼:
# Python3 code to demonstrate
# removing duplicate sublist
# using set() + sorted()
# initializing list
test_list = [[1, 0, -1], [-1, 0, 1], [-1, 0, 1],
[1, 2, 3], [3, 4, 1]]
# printing original list
print("The original list : " + str(test_list))
# using set() + sorted()
# removing duplicate sublist
res = list(set(tuple(sorted(sub)) for sub in test_list))
# print result
print("The list after duplicate removal : " + str(res))
→ 輸出結(jié)果:
The original list : [[1, 0, -1], [-1, 0, 1], [-1, 0, 1], [1, 2, 3], [3, 4, 1]]
The list after duplicate removal : [(-1, 0, 1), (1, 3, 4), (1, 2, 3)]
也可以利用 set() + map() + sorted()
示例代碼:
# Python3 code to demonstrate
# removing duplicate sublist
# using set() + map() + sorted()
# initializing list
test_list = [[1, 0, -1], [-1, 0, 1], [-1, 0, 1],
[1, 2, 3], [3, 4, 1]]
# printing original list
print("The original list : " + str(test_list))
# using set() + map() + sorted()
# removing duplicate sublist
res = list(set(map(lambda i: tuple(sorted(i)), test_list)))
# print result
print("The list after duplicate removal : " + str(res))
→ 輸出結(jié)果:
The original list : [[1, 0, -1], [-1, 0, 1], [-1, 0, 1], [1, 2, 3], [3, 4, 1]]
The list after duplicate removal : [(-1, 0, 1), (1, 3, 4), (1, 2, 3)]
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