Pandas DataFrame to JSON: Customizing Output with to_json()

Maximizing Data Integrity: A Step-by-Step Guide to Appending DataFrames to Excel Files Using Python's append_df_to_excel Function

Calculating Percentiles in Python: A Simplified Approach

Understanding Dynamic Paths with Python Pandas and Creating a CSV File for Flexible Data Storage

Understanding Attribute Errors in Python: A Case Study on Pandas DataFrames

Understanding the Correct Encoding for CSV Output with Chinese Characters

Working with Datetime Columns in pandas: A Deep Dive

To calculate the sum of sales for each salesman in a month before their training date, we need to group by "salesman" and "transaction_month", then apply the aggregation function `sum` to the 'sales' column.

Avoiding NaN Values When Adding Columns to DataFrames

Merging Excel Sheets in Pandas with Different Dimensions: A Comprehensive Guide