GroupBy: split-apply-combine, The pandas development team, 2024 - Official guide to Pandas groupby operations, covering the split-apply-combine pattern and various aggregation, transformation, and filtering methods.
Python for Data Analysis, Wes McKinney, 2022 (O'Reilly Media) - A comprehensive guide by the creator of Pandas, providing in-depth coverage of data manipulation, including groupby and aggregation techniques.