ZhangZhihuiAAA - 博客园

Pandas - How to sort a dataframe by a column?

摘要： To sort a Pandas DataFrame by a column, use sort_values(). Here are the common usages: 1. Sort by one column df_sorted = df.sort_values(by="column_nam 阅读全文

posted @ 2025-11-23 08:01 ZhangZhihuiAAA 阅读(6) 评论(0) 推荐(0)

PySpark - Read Data from PostgreSQL

摘要： jdbc_url = "jdbc:postgresql://localhost:5432/postgres" properties = { "user": "postgres", "password": "postgrespwd", "driver": "org.postgresql.Driver" 阅读全文

posted @ 2025-11-22 21:47 ZhangZhihuiAAA 阅读(5) 评论(0) 推荐(0)

PySpark - TypeError: 'JavaPackage' object is not callable

摘要： Spark installed on WSL. Java installed on WSL. Jupyter ran on WSL: jupyter-lab --no-browser Code ran in Windows browser: spark = (SparkSession.builder 阅读全文

posted @ 2025-11-22 20:54 ZhangZhihuiAAA 阅读(16) 评论(0) 推荐(0)

Github - Password authentication is not supported for Git operations

摘要： remote: Invalid username or token. Password authentication is not supported for Git operations.fatal: Authentication failed for 'https://github.com/Zh 阅读全文

posted @ 2025-11-21 15:27 ZhangZhihuiAAA 阅读(10) 评论(0) 推荐(0)

Matplotlib - gca() and gcf()

摘要： plt.gca().xaxis.set_major_formatter(plt.matplotlib.dates.DateFormatter('%b %Y')) Please tell me about the gca() function in matplotlib. plt.gca() 是 Ma 阅读全文

posted @ 2025-11-21 08:36 ZhangZhihuiAAA 阅读(9) 评论(0) 推荐(0)

Pandas - Long Format and Wide Format

摘要： What's the difference between long format and wide format? Which one is the default in Pandas? ChatGPT said: Here is the clear difference and what Pan 阅读全文

posted @ 2025-11-20 09:09 ZhangZhihuiAAA 阅读(3) 评论(0) 推荐(0)

SQL - How to use count() window function?

摘要： Here’s a clear and practical explanation of how to use COUNT() as a window function in SQL, with examples for common databases such as PostgreSQL, MyS 阅读全文

posted @ 2025-11-19 16:34 ZhangZhihuiAAA 阅读(7) 评论(0) 推荐(0)

为什么求方差和标准差至少需要两个数据点？

摘要：因为方差（variance）和标准差（standard deviation）衡量的是“数据的离散程度”，而离散程度至少需要两个数据点才能体现。下面从数学和直觉两个角度解释： ✅ 1. 直觉解释：至少需要两点才能体现“差异” 一个数据点只能告诉你“它自己是多少”。要知道数据是否“分散”，你至少需要比阅读全文

posted @ 2025-11-19 16:02 ZhangZhihuiAAA 阅读(11) 评论(0) 推荐(0)

Python - Don't forget the ',' when define a tuple

摘要： root_ids = ('abcd') root_ids_tuple = ('abcd',) root_ids_list = ['abcd'] print(type(root_ids)) print(' ') print([f"'{item}'" for item in root_ids]) pri 阅读全文

posted @ 2025-11-17 14:06 ZhangZhihuiAAA 阅读(7) 评论(0) 推荐(0)

Spark SQL - Recursive CTE example

摘要： WITH RECURSIVE filtered_org_ids AS ( SELECT organizationresourceid, parentresourceid FROM tmp_org WHERE organizationresourceid = '123456' UNION SELECT 阅读全文

posted @ 2025-11-17 10:38 ZhangZhihuiAAA 阅读(58) 评论(0) 推荐(0)

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