Indexing and selecting data, The pandas development team, 2024 - Provides comprehensive coverage of label-based (.loc) and position-based (.iloc) indexing, including the rationale for their separation and the deprecation of .ix.
Python Data Science Handbook: Essential Tools for Working with Data, Jake VanderPlas, 2016 (O'Reilly Media) - A widely referenced resource that clearly explains Pandas data indexing and selection, contrasting label-based (.loc) and integer-position-based (.iloc) methods.