Backend Development
Python Tutorial
Simply master the usage of the counter structure in Python's Collections module
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)
""" 
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1378
52
The 2-Hour Python Plan: A Realistic Approach
Apr 11, 2025 am 12:04 AM
You can learn basic programming concepts and skills of Python within 2 hours. 1. Learn variables and data types, 2. Master control flow (conditional statements and loops), 3. Understand the definition and use of functions, 4. Quickly get started with Python programming through simple examples and code snippets.
Python: Exploring Its Primary Applications
Apr 10, 2025 am 09:41 AM
Python is widely used in the fields of web development, data science, machine learning, automation and scripting. 1) In web development, Django and Flask frameworks simplify the development process. 2) In the fields of data science and machine learning, NumPy, Pandas, Scikit-learn and TensorFlow libraries provide strong support. 3) In terms of automation and scripting, Python is suitable for tasks such as automated testing and system management.
How to read redis queue
Apr 10, 2025 pm 10:12 PM
To read a queue from Redis, you need to get the queue name, read the elements using the LPOP command, and process the empty queue. The specific steps are as follows: Get the queue name: name it with the prefix of "queue:" such as "queue:my-queue". Use the LPOP command: Eject the element from the head of the queue and return its value, such as LPOP queue:my-queue. Processing empty queues: If the queue is empty, LPOP returns nil, and you can check whether the queue exists before reading the element.
How to view server version of Redis
Apr 10, 2025 pm 01:27 PM
Question: How to view the Redis server version? Use the command line tool redis-cli --version to view the version of the connected server. Use the INFO server command to view the server's internal version and need to parse and return information. In a cluster environment, check the version consistency of each node and can be automatically checked using scripts. Use scripts to automate viewing versions, such as connecting with Python scripts and printing version information.
How to start the server with redis
Apr 10, 2025 pm 08:12 PM
The steps to start a Redis server include: Install Redis according to the operating system. Start the Redis service via redis-server (Linux/macOS) or redis-server.exe (Windows). Use the redis-cli ping (Linux/macOS) or redis-cli.exe ping (Windows) command to check the service status. Use a Redis client, such as redis-cli, Python, or Node.js, to access the server.
How to set the Redis memory size according to business needs?
Apr 10, 2025 pm 02:18 PM
Redis memory size setting needs to consider the following factors: data volume and growth trend: Estimate the size and growth rate of stored data. Data type: Different types (such as lists, hashes) occupy different memory. Caching policy: Full cache, partial cache, and phasing policies affect memory usage. Business Peak: Leave enough memory to deal with traffic peaks.
What is the impact of Redis persistence on memory?
Apr 10, 2025 pm 02:15 PM
Redis persistence will take up extra memory, RDB temporarily increases memory usage when generating snapshots, and AOF continues to take up memory when appending logs. Influencing factors include data volume, persistence policy and Redis configuration. To mitigate the impact, you can reasonably configure RDB snapshot policies, optimize AOF configuration, upgrade hardware and monitor memory usage. Furthermore, it is crucial to find a balance between performance and data security.
Python vs. C : Applications and Use Cases Compared
Apr 12, 2025 am 12:01 AM
Python is suitable for data science, web development and automation tasks, while C is suitable for system programming, game development and embedded systems. Python is known for its simplicity and powerful ecosystem, while C is known for its high performance and underlying control capabilities.
