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list的基礎(chǔ)上，將第一個出現(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 listtest_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 listtest_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 listtest_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 orderingprint ('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改變。

示例代碼：

# Python 3 code to demonstrate # removing duplicated from list # using list comprehension + enumerate() # initializing listtest_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 listtest_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 listtest_list = [[1, 0, -1], [-1, 0, 1], [-1, 0, 1], [1, 2, 3], [3, 4, 1]] # printing original listprint('The original list : ' + str(test_list)) # using set() + sorted()# removing duplicate sublistres = list(set(tuple(sorted(sub)) for sub in test_list)) # print resultprint('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 listtest_list = [[1, 0, -1], [-1, 0, 1], [-1, 0, 1], [1, 2, 3], [3, 4, 1]] # printing original listprint('The original list : ' + str(test_list)) # using set() + map() + sorted()# removing duplicate sublistres = list(set(map(lambda i: tuple(sorted(i)), test_list))) # print resultprint('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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