LINQ Tutorial: Master the Key C# Library

Discover what LINQ is and how it enables querying across collections with filtering, ordering, and transforming data. Write your first LINQ query using lambda expressions in C# with System.Linq namespace.

Discover how extension methods let LINQ enhance IEnumerable with the Where filter by importing System.Linq, and see static extension methods on strings that behave like native members.

Learn how LINQ extension methods operate on IEnumerable<T>, producing new collections without modifying the input, and how method chaining combines where and orderby into elegant, fluent queries.

Learn how deferred execution in LINQ delays query evaluation until needed, enabling up-to-date results and performance gains via materialization with ToList, Where, and Take.

Compare method syntax and query syntax in LINQ, explore their differences and trade-offs, and see how duplicates and joins are handled across both approaches.

Learn how the all method in LINQ verifies that every element meets a predicate, with examples like all numbers greater than zero and all pets have non-empty names.

Explore using Count and LongCount in LINQ to tally collection elements that match a predicate, including dogs lighter than ten kilograms and pets named Bruce; understand int versus long results.

Learn how Linq's contains method checks for an element in a collection and how equality comparer behavior—default and custom by id—affects matches.

Master LINQ ordering in C# by using OrderBy and OrderByDescending, chaining ThenBy and ThenByDescending, and optionally custom comparers with IComparer, while understanding key selectors, and the Reverse method.

Use Min and Max to find smallest and largest values, using selectors for weights. Learn why parameterless Min/Max require IComparable and how empty collections behave for non-nullable and nullable types.

Learn how to use the average method in linq to compute the mean of numeric collections in C#, using a selector with a lambda to target a numeric value.

Learn to use the sum method to add numeric values in a collection, optionally via a selector, and compare its behavior to average, including handling of empty collections returning zero.