[英]Most Efficient way to calculate Frequency of values in a Python list?
I am looking for a fast and efficient way to calculate the frequency of list
items in python: 我正在寻找一种快速有效的方法来计算python中list
项的频率:
list = ['a','b','a','b', ......]
I want a frequency counter which would give me an output like this: 我想要一个频率计数器,它会给我一个像这样的输出:
[ ('a', 10),('b', 8) ...]
The items should be arranged in descending order of frequency as shown above. 如上所示,项目应按频率的降序排列。
Python2.7+ Python2.7 +
>>> from collections import Counter
>>> L=['a','b','a','b']
>>> print(Counter(L))
Counter({'a': 2, 'b': 2})
>>> print(Counter(L).items())
dict_items([('a', 2), ('b', 2)])
python2.5/2.6 的python2.5 / 2.6
>>> from collections import defaultdict
>>> L=['a','b','a','b']
>>> d=defaultdict(int)
>>> for item in L:
>>> d[item]+=1
>>>
>>> print d
defaultdict(<type 'int'>, {'a': 2, 'b': 2})
>>> print d.items()
[('a', 2), ('b', 2)]
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