[파이썬] count, Counter with dictionary

list.count()

# list.count() 메서드를 이용.
some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']
duplicates = set()
for each in set(some_list):
    if some_list.count(each) > 1:
        duplicates.add(each)
print(duplicates)

# 컴프리헨션으로 정리
duplicates = set(each for each in set(some_list) if some_list.count(each) > 1)
print(duplicates)

 

dictionary

# 딕셔너리를 이용.
some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']
counter = {}
for each in some_list:
    counter.setdefault(each, 0)
    counter[each] += 1
duplicates = set()
for key, value in counter.items():
    if value > 1:
        duplicates.add(key)
print(duplicates)

 

조금 더 단순하게... 

some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']

counter = {}
duplicates = set()

for each in some_list:
    counter.setdefault(each, 0)
    counter[each] += 1
    if counter[each] > 1:
        duplicates.add(each)

print(duplicates)

 

collections.Counter()

# collections 패키지의 Counter와 컴프리헨션으로 정리.

from collections import Counter


some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']
counter = Counter(some_list)
duplicates = set(k for k, v in Counter(some_list).items() if v > 1)
print(duplicates)