.NET API Documentation

Class Overview

The System.Linq.Enumerable class provides a set of static extension methods that operate on IEnumerable<T> objects. These methods are the core of Language Integrated Query (LINQ) and enable powerful data manipulation and querying capabilities directly within C# and Visual Basic code.

This class contains methods for filtering, projecting, ordering, grouping, and performing aggregate operations on sequences. It's fundamental for working with collections in a declarative and expressive way.

Members

• All<TSource>(IEnumerable<TSource>, Func<TSource, bool>)

  bool All<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)

  Tests whether all elements of a sequence satisfy a condition.

  Parameters:

  source: System.Collections.Generic.IEnumerable<TSource>
  An IEnumerable<T> whose elements to test for all matching the condition.

  predicate: System.Func<TSource, bool>
  A function to test each element for a condition.

  Returns:

  true if all elements in the sequence pass the test in the specified predicate, or if the sequence is empty; otherwise, false.

  Remarks:

  If source is empty, All returns true.

  Example:

  // Define a list of integers var numbers = new List { 2, 4, 6, 8, 10 }; // Check if all numbers are even bool allEven = numbers.All(n => n % 2 == 0); // Output: True Console.WriteLine(allEven);

• Any<TSource>(IEnumerable<TSource>, Func<TSource, bool>)

  bool Any<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)

  Tests whether any element of a sequence satisfies a condition.

  Parameters:

  source: System.Collections.Generic.IEnumerable<TSource>
  An IEnumerable<T> whose elements to test for any matching the condition.

  predicate: System.Func<TSource, bool>
  A function to test each element for a condition.

  Returns:

  true if any element of the sequence passes the test in the specified predicate; otherwise, false.

  Remarks:

  If source is empty, Any returns false.

  Example:

  // Define a list of integers var numbers = new List { 1, 3, 5, 7, 9 }; // Check if any number is even bool anyEven = numbers.Any(n => n % 2 == 0); // Output: False Console.WriteLine(anyEven);

• Count<TSource>(IEnumerable<TSource>)

  int Count<TSource>(this IEnumerable<TSource> source)

  Returns the number of elements in a sequence.

  Parameters:

  source: System.Collections.Generic.IEnumerable<TSource>
  The IEnumerable<T> that contains the elements to be counted.

  Returns:

  The number of elements in the sequence.

  Remarks:

  If source implements ICollection<T>, that implementation's Count property is returned. Otherwise, this method iterates through the sequence and counts its elements.

  Example:

  var names = new List<string> { "Alice", "Bob", "Charlie" }; int count = names.Count(); // Output: 3 Console.WriteLine(count);

• Where<TSource>(IEnumerable<TSource>, Func<TSource, bool>)

  IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)

  Filters a sequence of values based on a predicate.

  Parameters:

  source: System.Collections.Generic.IEnumerable<TSource>
  An IEnumerable<T> to filter.

  predicate: System.Func<TSource, bool>
  A function to test each element for a condition.

  Returns:

  An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.

  Example:

  var numbers = new List<int> { 1, 2, 3, 4, 5, 6 }; var evenNumbers = numbers.Where(n => n % 2 == 0); // Output: 2, 4, 6 foreach (var num in evenNumbers) { Console.Write($"{num} "); } Console.WriteLine();

• Select<TSource, TResult>(IEnumerable<TSource>, Func<TSource, TResult>)

  IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)

  Projects each element of a sequence into a new form.

  Parameters:

  source: System.Collections.Generic.IEnumerable<TSource>
  A sequence of values to invoke a transform function on.

  selector: System.Func<TSource, TResult>
  A transform function to apply to each element.

  Returns:

  An IEnumerable<TResult> whose elements are the result of invoking the transform function on each element of the given sequence.

  Example:

  var words = new List<string> { "apple", "banana", "cherry" }; var lengths = words.Select(w => w.Length); // Output: 5, 6, 6 foreach (var len in lengths) { Console.Write($"{len} "); } Console.WriteLine();

• OrderBy<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>)

  IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)

  Sorts the elements of a sequence in ascending order according to a key.

  Parameters:

  source: System.Collections.Generic.IEnumerable<TSource>
  The sequence of values to order.

  keySelector: System.Func<TSource, TKey>
  A function to extract a key from each element.

  Returns:

  An IOrderedEnumerable<TSource> whose elements are sorted in ascending order by key.

  Example:

  var products = new List<Product> { new Product { Name = "Laptop", Price = 1200 }, new Product { Name = "Keyboard", Price = 75 }, new Product { Name = "Mouse", Price = 25 } }; var sortedProducts = products.OrderBy(p => p.Price); // Output: Mouse (25), Keyboard (75), Laptop (1200) foreach (var p in sortedProducts) { Console.WriteLine($"{p.Name} ({p.Price})"); }

• GroupBy<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>)

  IEnumerable<IGrouping<TKey, TSource>> GroupBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)

  Groups the elements of a sequence by a specified key selector.

  Parameters:

  source: System.Collections.Generic.IEnumerable<TSource>
  The sequence of values to group.

  keySelector: System.Func<TSource, TKey>
  A function to extract the key from each element.

  Returns:

  An IEnumerable<T> of IGrouping<TKey, TSource>, where each group represents a unique key.

  Example:

  var people = new List<Person> { new Person { Name = "Alice", City = "New York" }, new Person { Name = "Bob", City = "London" }, new Person { Name = "Charlie", City = "New York" }, new Person { Name = "David", City = "London" } }; var groupedByCity = people.GroupBy(p => p.City); foreach (var group in groupedByCity) { Console.WriteLine($"City: {group.Key}"); foreach (var person in group) { Console.WriteLine($"- {person.Name}"); } } // Output: // City: New York // - Alice // - Charlie // City: London // - Bob // - David