Examples of Common Linq Expressions [closed]

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When I'm writing code, I'm starting to identify those places where I could use Linq. My problem is that I'm still very new to the syntax. I learn best through examples, but I can't seem to easily find the example I need.

I wanted to start this thread to create a repository of common Linq expressions that others could stumble upon via google.

The question: can you provide any examples of Linq expressions you use for common tasks?

For example, I've already written the following:

• searching a list
• summing an array
• summing a certain property in a collection of elements

To get the thread started, I'll post an answer that contains these.

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Enumerating through a list to find a certain element

tboShippingLotNumber existingLotNumber =
    (tboShippingLotNumber)(from lot in shipmentDetailLine.LotNumbers
                           where 
                               (lot.LotNumber == lotNumber) &&
                               (lot.ShipLineKey == shipmentDetailLine.Key)
                           select lot).ElementAtOrDefault(0);

if (existingLotNumber == null)
{
    // not found exception
}

Summing an array:

decimal[] array = { 1.5m, 2.5m, 3.5m };
decimal sum = array.Sum();

Summing a certain property in a list of objects

decimal sum = (from shipment in _ShipmentData.Shipments select 
    shipment.AmountShipped).Sum()

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Covered most of the Linq examples

using System;
using System.Linq;
using System.Collections.Generic;

namespace LinqExamples
{
    // https://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b
    class Program
    {
        static void Main(string[] args)
        {
            loadData();
            // Print all the subjects
            Console.WriteLine("------------------(SelectMany) Print all the subjects--------------------");
            Console.WriteLine(string.Join("\n", students.SelectMany(s => s.subjects).Distinct()));

            // Sort by first subject and then by first name
            Console.WriteLine("\n------------------(OrderBy ThenBy) Sort by first subject and then by first name--------------------");
            Console.WriteLine(string.Join("\n", students.OrderBy(x => x.subjects[0]).ThenBy(m => m.FirstName)));

            Console.WriteLine("\n------------------Group by first subject and then no of student oppted for the subject--------------------");
            Console.WriteLine(string.Join("\n", students.GroupBy(x => x.subjects[0]).Select(s => new { Subject = s.Key, count = s.Count() })));
            foreach (var g in students.GroupBy(x => x.subjects[0]).Select(s => new { Subject = s.Key, count = s.Count(), studentFirstName = s.Select(x => x.FirstName) }))
            {
                Console.WriteLine("Subject: {0}, Total Student: {1}, Student FirstNames: {2}", g.Subject, g.count, string.Join(", ", g.studentFirstName));
            }

            string wordsString = "This is the same book which all the student used to read";
            Console.WriteLine(string.Join("\n", wordsString.Split(' ').GroupBy(x => x).Select(s => new { Word = s.Key, count = s.Count() })));

            Console.WriteLine("\n------------------(OrderByDescending) Top 2 Salary--------------------");
            Console.WriteLine(string.Join("\n", students.OrderByDescending(s => s.Salary).Take(2)));

            Console.WriteLine("\n------------------Distinct--------------------");
            int[] arr = { 2, 2, 3, 5, 5 };
            Console.WriteLine($"[{string.Join(", ", arr)}]");
            Console.WriteLine(string.Join(", ", arr.Distinct()));

            Console.WriteLine("\n------------------(Union) Unique numbers from both arrays--------------------");
            int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };
            int[] numbersB = { 1, 3, 5, 7, 8 };
            Console.WriteLine($"[{string.Join(", ", numbersA)}]");
            Console.WriteLine($"[{string.Join(", ", numbersB)}]");
            Console.WriteLine(string.Join(", ", numbersA.Union(numbersB).OrderBy(x => x)));

            Console.WriteLine("\n------------------(Intersect) Common numbers shared by both arrays--------------------");
            Console.WriteLine($"[{string.Join(", ", numbersA)}]");
            Console.WriteLine($"[{string.Join(", ", numbersB)}]");
            Console.WriteLine(string.Join(", ", numbersA.Intersect(numbersB).OrderBy(x => x)));

            Console.WriteLine("\n------------------(Except) Numbers in first array but not second array--------------------");
            Console.WriteLine($"[{string.Join(", ", numbersA)}]");
            Console.WriteLine($"[{string.Join(", ", numbersB)}]");
            Console.WriteLine(string.Join(", ", numbersA.Except(numbersB).OrderBy(x => x)));

            Console.WriteLine("\n------------------Concat numbers from both arrays--------------------");
            Console.WriteLine($"[{string.Join(", ", numbersA)}]");
            Console.WriteLine($"[{string.Join(", ", numbersB)}]");
            Console.WriteLine(string.Join(", ", numbersA.Concat(numbersB).OrderBy(x => x)));

            Console.WriteLine("\n------------------ToDictionary--------------------");
            var scoreRecords = new[] { new {Name = "Alice", Score = 50},
                                new {Name = "Bob"  , Score = 40},
                                new {Name = "Cathy", Score = 45}
                            };
            var scoreRecordsDict = scoreRecords.ToDictionary(sr => sr.Name);
            Console.WriteLine("Bob's score: {0}", scoreRecordsDict["Bob"]);

            Console.WriteLine("\n------------------OfType--------------------");
            object[] numbers = { null, 1.0, "two", 3, "four", 5, "six", 7.0, true };
            Console.WriteLine($"[{string.Join(", ", numbers)}]");
            var doubles = numbers.OfType<double>();
            Console.WriteLine("Numbers stored as doubles: " + string.Join(", ", numbers.OfType<double>()));
            Console.WriteLine("Numbers stored as bool: " + string.Join(", ", numbers.OfType<bool>()));
            Console.WriteLine("Numbers stored as string: " + string.Join(", ", numbers.OfType<string>()));
            Console.WriteLine("Numbers stored as int: " + string.Join(", ", numbers.OfType<int>()));

            Console.WriteLine("\n------------------First with Condition--------------------");
            string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };
            Console.WriteLine($"[{string.Join(", ", strings)}]");
            Console.WriteLine("A string starting with 'o': {0}", strings.FirstOrDefault(s => s[0] == 'o'));

            Console.WriteLine("\n------------------GroupBy with Condition--------------------");
            int[] num = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
            Console.WriteLine($"[{string.Join(", ", num)}]");
            var numberGroups = num.GroupBy(x => x % 5).Select(g => new { Remainder = g.Key, Numbers = g });
            foreach (var g in numberGroups)
            {
                Console.WriteLine("Numbers with a remainder of {0} when divided by 5: {1}", g.Remainder, string.Join(", ", g.Numbers));
            }

            Console.WriteLine("\n------------------Range--------------------");
            Console.WriteLine(string.Join(", ", Enumerable.Range(1, 5)));

            Console.WriteLine($"\n{string.Join("", Enumerable.Repeat('-', 18))}Repeat{string.Join("", Enumerable.Repeat('-', 18))}");
            Console.WriteLine("Repeat(Print) '*' for 5 times: " + string.Join("", Enumerable.Repeat('*', 5)));

            Console.WriteLine("\n------------------Any--------------------");
            string[] words = { "believe", "relief", "receipt", "field" };
            Console.WriteLine($"[{string.Join(", ", words)}]");
            Console.WriteLine("Is there any word which contains 'ei': {0}", words.Any(w => w.Contains("ei")));
            Console.WriteLine("Is there any word which start with 'f': {0}", words.Any(w => w[0] == 'f'));
            Console.WriteLine("Is there any word which start with 'n': {0}", words.Any(w => w[0] == 'n'));

            Console.WriteLine("\n------------------All--------------------");
            int[] nos = { 1, 11, 3, 19, 41, 65, 19 };
            Console.WriteLine($"[{string.Join(", ", nos)}]");
            Console.WriteLine("The list contains only odd numbers: {0}", nos.All(n => n % 2 == 1));
            Console.WriteLine("The list contains only even numbers: {0}", nos.All(n => n % 2 == 0));


            Console.WriteLine("\n------------------Where with index --------------------");
            string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };
            Console.WriteLine($"[{string.Join(", ", digits)}]");

            var shortDigits = digits.Where((digit, index) => digit.Length < index);
            Console.WriteLine(string.Join(" is shorter in length than its index position\n", shortDigits));

            Console.WriteLine("\n------------------Select with index --------------------");
            Console.WriteLine($"[{string.Join(", ", digits)}]");
            foreach (var n in digits.Select((x, indexi) => new { word = x, InPlace = indexi }))
            {
                Console.WriteLine("{0}: {1}", n.word, n.InPlace);
            }

            Console.WriteLine("\n------------------SequenceEqual (all array element matches in the same order)--------------------");
            var wordsA = new string[] { "cherry", "apple", "blueberry" };
            var wordsB = new string[] { "cherry", "apple", "blueberry" };
            Console.WriteLine($"[{string.Join(", ", wordsA)}]");
            Console.WriteLine($"[{string.Join(", ", wordsB)}]");
            Console.WriteLine("The sequences match: {0}", wordsA.SequenceEqual(wordsB));
        }

        private static void loadData()
        {
            students.Add(new Student("English", "Math"));
            students.Add(new Student("Physics", "Math"));
            students.Add(new Student("Chemistry", "Math"));
            students.Add(new Student("English", "Hindi"));
            students.Add(new Student("GK", "Science"));
            students.Add(new Student("English", "Math"));
            students.Add(new Student("Physics", "Math"));
            students.Add(new Student("Chemistry", "Math"));
            students.Add(new Student("English", "Hindi"));
            students.Add(new Student("GK", "Science"));
        }

        public static List<Student> students = new List<Student>();
    }

    public class Student
    {
        public string FirstName { get; set; } = Faker.Name.First();
        public string LastName { get; set; } = Faker.Name.Last();
        public string Mobile { get; set; } = Faker.Phone.Number();
        public int Salary { get; set; } = Faker.RandomNumber.Next(1000, 10000);
        public Guid Id { get; set; } = Guid.NewGuid();
        public List<string> subjects = new List<string>();
        public Student(params string[] subjects)
        {
            foreach (var sub in subjects)
            {
                this.subjects.Add(sub);
            }
        }

        public override string ToString()
        {
            return $"{this.FirstName} {this.LastName} {this.Salary}\t{this.subjects[0]}, {this.subjects[1]} {this.Mobile}";
        }
    }
}