linq-beginner.md

LINQ Basics

• Select (Projection): Transforms each element in a collection.

  var uppercaseNames = names.Select(name => name.ToUpper());

• Where (Filtering): Filters a sequence based on a predicate.

  var evenNumbers = numbers.Where(num => num % 2 == 0);

• OrderBy / OrderByDescending (Sorting): Sorts elements in ascending or descending order.

  var sortedNames = names.OrderBy(name => name);
  var sortedNumbersDesc = numbers.OrderByDescending(num => num);

Element Operations

• First / FirstOrDefault: Returns the first element, or a default value if the sequence is empty.

  var firstNumber = numbers.First();
  var firstOrDefault = numbers.FirstOrDefault();

• Single / SingleOrDefault: Expects a single element and throws an exception if there is more than one.

  var singleNumber = numbers.Single();
  var singleOrDefault = numbers.SingleOrDefault();

Aggregation

• Count: Counts the elements that satisfy a condition.

  var numberOfEvens = numbers.Count(num => num % 2 == 0);

• Sum: Computes the sum of a sequence.

  var total = numbers.Sum();

• Average: Computes the average of a sequence.

  var average = numbers.Average();

Set Operations

• Distinct: Removes duplicate elements.

  var distinctNumbers = numbers.Distinct();

• Union: Produces the set union of two sequences.

  var combinedNumbers = firstList.Union(secondList);

• Intersect: Produces the set intersection of two sequences.

  var commonNumbers = firstList.Intersect(secondList);

• Except: Produces the set difference of two sequences.

  var uniqueToFirstList = firstList.Except(secondList);

Conversion

• ToArray: Converts a sequence to an array.

  var array = numbers.ToArray();

• ToList: Converts a sequence to a list.

  var list = numbers.ToList();

• ToDictionary: Converts a sequence to a dictionary.

  var dictionary = numbers.ToDictionary(num => num, num => num * num);

Quantifiers

• Any: Checks if any elements satisfy a condition.

  var hasEvens = numbers.Any(num => num % 2 == 0);

• All: Checks if all elements satisfy a condition.

  var allPositive = numbers.All(num => num > 0);

Generation

• Range: Generates a sequence of numbers within a specified range.

  var range = Enumerable.Range(1, 10);

• Repeat: Generates a sequence that contains one repeated value.

  var repeated = Enumerable.Repeat("Hello", 5);

This cheat sheet covers the essentials, but LINQ is a powerful tool with many more methods and nuances.