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Video Description
Ready to level up? GroupBy turns raw data into insights. Join combines datasets. And understanding execution timing keeps your code fast.
What you'll learn:
- GroupBy - organize flat data into logical groups
- The Key property and why it matters
- Join - combining two collections on matching keys
- Inner join behavior (what happens to non-matches)
- OrderBy + ThenBy for multi-level sorting
- The OrderBy trap everyone falls into
- Sum, Count, Average, Min, Max aggregates
- Deferred vs immediate execution (the full picture)
- Multiple enumeration - the #1 performance killer
- ToList() as your execution snapshot
Key insights:
- GroupBy + aggregates = instant data analysis
- Each group IS a collection you can query
- ThenBy adds secondary sorting (OrderBy replaces!)
- Methods returning IEnumerable are deferred
- Execute once with ToList(), reuse many times
- Filter before sorting (Where before OrderBy)
- Any() beats Count() for existence checks
We'll build:
- Customer order summaries with GroupBy
- Multi-table joins (customers + orders)
- Sales dashboard with multiple aggregations
- Performance-optimized query patterns
Next Video: Introduction to Multithreading
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Timestamps
Chapters
- 0:00 More LINQ Power
- 1:15 GroupBy - The Game Changer
- 2:19 GroupBy Visual Example
- 3:02 Join - Combining Two Datasets
- 3:53 Join Visual Example
- 4:35 OrderBy and ThenBy - Multi-Level Sorting
- 5:31 Don't do this with OrderBy!
- 6:02 Aggregate Functions - Sum, Count, Average
- 6:49 GroupBy with Aggregates
- 7:33 Lazy evaluation matters!
- 7:52 Deferred vs Immediate Execution
- 8:38 The Multiple Enumeration Problem
- 9:09 LINQ Performance Best Practices
- 10:16 Real-World Example: Sales Dashboard
- 10:44 Key Takeaways
- 11:46 Practice Challenge
Video Info
- Duration: 13:23
- Published: December 05, 2025
