GroupBy & Aggregation

What this module covers

By the end of it

• Explain split-apply-combine and what groupby returns before aggregation
• Aggregate with single functions, multiple functions, and named outputs
• Group by multiple keys and navigate the resulting MultiIndex
• Use transform to broadcast group statistics back to every row
• Use filter to keep or drop entire groups by a condition
• Apply custom functions with agg and apply, and know the difference
• Compute window functions: rolling, expanding, and grouped cumulative operations
• Avoid the common performance and correctness traps