Simply master the usage of the counter structure in Python's Collections module

Counter is a special dictionary, mainly used for counting. The key is the item to be counted, and the value stores the number.

from collections import Counter

>>> c = Counter('hello,world')
Counter({'l': 3, 'o': 2, 'e': 1, 'd': 1, 'h': 1, ',': 1, 'r': 1, 'w': 1})

Three types of parameters can be passed in for initialization: dictionaries, other iterable data types, and named parameter pairs.

 | __init__(self, iterable=None, **kwds)
 |  Create a new, empty Counter object. And if given, count elements
 |  from an input iterable. Or, initialize the count from another mapping
 |  of elements to their counts.
 |
 |  >>> c = Counter()       # a new, empty counter
 |  >>> c = Counter('gallahad')     # a new counter from an iterable
 |  >>> c = Counter({'a': 4, 'b': 2})   # a new counter from a mapping
 |  >>> c = Counter(a=4, b=2)     # a new counter from keyword args

Under the default request, accessing an item that does not exist will return 0. Counter can be used to count the occurrence of certain data, such as the frequency of each number in a long string of numbers = "67642192097348921647512014651027586741512651":

>>> c = Counter(numbers) # c 存储了每个数字的频率
>>> c.most_common()  # 所有数字按照频率排序。如果 most_common 接受了 int 参数 n，将返回频率前n 的数据，否则会返回所有的数据
[('1', 8),
 ('2', 6),
 ('6', 6),
 ('5', 5),
 ('4', 5),
 ('7', 5),
 ('0', 3),
 ('9', 3),
 ('8', 2),
 ('3', 1)]

In addition, you can also perform +, -, min, max and other operations on two Counter objects.

Comprehensive example:

print('Counter类型的应用') 
c = Counter("dengjingdong") 
#c = Counter({'n': 3, 'g': 3, 'd': 2, 'i': 1, 'o': 1, 'e': 1, 'j': 1}) 
print("原始数据：",c) 
print("最多的两个元素：",c.most_common(2))#输出数量最多的元素 
print("d的个数：",c['d'])#输出d的个数 
print(c.values())#输出字典的value列表 
print(sum(c.values()))#输出总字符数 
print(sorted(c.elements()))#将字典中的数据，按字典序排序 
print('\n\n') 
""" 
#删除所有d元素 
del c['d'] 
b = Counter("dengxiaoxiao") 
#通过subtract函数删除元素，元素个数可以变成负数。 
c.subtract(b) 
""" 
 
""" 
可以添加数据 
b = Counter("qinghuabeida") 
c.update(b) 
"""