Collection

from collections import Counter

Init signature: Counter(*args, **kwds)

Docstring:

Dict subclass for counting hashable items. Sometimes called a bag or multiset. Elements are stored as dictionary keys and their counts are stored as dictionary values.

返回值:Counter字典

c = Counter('abcdeabcdabcaba')  # count elements from a string
>>> print(c)    
Counter({'a': 5, 'b': 4, 'c': 3, 'd': 2, 'e': 1})

List the n most common elements and their counts from the most common to the least. If n is None, then list all element counts.

>>> c.most_common()        #  没有传递参数时,输出所有的要素
[('a', 5), ('b', 4), ('c', 3), ('d', 2), ('e', 1)]
>>> c.most_common(3)      # three most common elements 最多的3个要素
[('a', 5), ('b', 4), ('c', 3)]

Return a new list containing all items from the iterable in ascending order.

按升序返回包含items的list

>>> sorted(c)              # list all unique elements
['a', 'b', 'c', 'd', 'e']

常规操作

>>> ''.join(sorted(c.elements()))   # list elements with repetitions
'aaaaabbbbcccdde'
>>> sum(c.values())                 # total of all counts
15

>>> c['a']                          # count of letter 'a'
5
>>> for elem in 'shazam':           # update counts from an iterable
...     c[elem] += 1                # by adding 1 to each element's count
>>> c['a']                          # now there are seven 'a'
7
>>> del c['b']                      # remove all 'b'
>>> c['b']                          # now there are zero 'b'
0

>>> d = Counter('simsalabim')       # make another counter
>>> c.update(d)                     # add in the second counter
>>> c['a']                          # now there are nine 'a'
9

>>> c.clear()                       # empty the counter
>>> c
Counter()

If a count is set to zero or reduced to zero, it will remain in the counter until the entry is deleted or the counter is cleared:

如果减少计数器的数值为0(或设定为0),但是元素不会消失,除非完全被释放.

>>> c = Counter('aaabbc')
>>> c['b'] -= 2                     # reduce the count of 'b' by two
>>> c.most_common()                 # 'b' is still in, but its count is zero
[('a', 3), ('c', 1), ('b', 0)]

>>> c = Counter()                           # a new, empty counter
>>> c = Counter('gallahad')                 # a new counter from an iterable
print(c)
Counter({'a': 3, 'l': 2, 'g': 1, 'h': 1, 'd': 1})
>>> c = Counter({'a': 4, 'b': 2})           # a new counter from a mapping
>>> c = Counter(a=4, b=2)                   # a new counter from keyword args
Counter({'a': 4, 'b': 2})
>>> c['g'] = 3
>>> c
Counter({'a': 4, 'b': 2, 'g': 3})