C# Development for Beginners #18: More LINQ Power - GroupBy, Join, and Performance Secrets
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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
Previous Video: LINQ - Query Your Data Next Video: Introduction to Multithreading ► Full Playlist: https://www.youtube.com/playlist?list=PLGxFXI4dC2shfDgudNdh1FtSLcAZG0-Ba ► Code Repository: https://github.com/benday-inc/csharp-for-beginners-2025
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Timestamps
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
