What it does:

Split-Apply-Combine—group data, compute stats, and merge results.

Key Concepts:

• Grouping: Split data by a key (e.g., "Country").
• Aggregation: Compute summaries (sum(), mean()).
• Transformation: Modify groups without collapsing (e.g., normalize).

Why it matters:

Enables complex aggregations (e.g., "average sales per region").