Kjell Slupphaug developed an inclusive aggregation feature for the statisticsnorway/ssb-fagfunksjoner repository, enabling DataFrames to aggregate across non-exclusive categories with grand totals. Using Python and Pandas, he implemented the all_combos_agg_inclusive function, which supports complex data analysis scenarios by handling overlapping groupings and ensuring accurate reporting. His approach included building a comprehensive test suite to validate edge cases, such as category mappings and NaN handling in observed versus predicted counts. He further refined the implementation by addressing deduplication after index resets, demonstrating attention to data integrity and robustness. The work reflects depth in both data analysis and testing practices.