Pandas User Guide: Basics - Column selection, addition, deletion, The Pandas Development Team, 2024 - The official documentation providing fundamental details on how to add and manipulate columns in a Pandas DataFrame, including constant assignment and derived columns.
Pandas User Guide: Basics - Alignment, The Pandas Development Team, 2024 - Explains the crucial concept of index alignment in Pandas, which clarifies how data is matched and how missing values (NaN) can arise when assigning Series with differing indices.
Python for Data Analysis, Wes McKinney, 2022 (O'Reilly Media) - A foundational book by the creator of Pandas, offering in-depth explanations and examples on data structures, data manipulation, including adding and transforming DataFrame columns.