[學習] Python List

常遇到的問題

find the duplicate elements in the list
count the duplicate elements in the list
remove the duplicate elements in the list

List.count() 用法

計算指定的值在 list 出現幾次

語法：list.count(element)

input:

1
2
3

my_list = [2, 3, 1, 4, 2, 5, 3, 7]
print(my_list.count(3))
print(my_list.count(7))

output:

1
2

2
1

進階

將 list 裡面所有的 element 都記錄下有幾個

input:

dup_list = ["a", "c", "a", "c", "b", "a"]
clear_dict = {i: dup_list.count(i) for i in dup_list}

print(clear_dict)

output:

1	{'a': 3, 'c': 2, 'b': 1}

另一種用法 Counter

需要先 import
語法：
from collections import Counter
Counter(List/String)

counter 出來的型態通常會轉成 Dictionary 會比較方便～
在下面也會示範有轉成 dict 跟沒轉成 dict 的差別

input:

from collections import Counter
dup_list = ["a", "c", "a", "c", "b", "a"]
count_list = dict(Counter(dup_list))
count_string = Counter('acacaba')

print(count_list)
print(count_string)

output:

1 2	{'a': 3, 'c': 2, 'b': 1} Counter({'a': 4, 'b': 1, 'c': 2})

Counter 的額外用法

找出出現次數前 n 多

語法： Counter.most_common()

input:

1
2
3

# 接續上一個例子
print(count_string.most_common(1))
print(count_string.most_common(2))

output:

1 2	[('a', 4)] [('a', 4), ('c', 2)]