Basic ways to use LINQ on collections.

LINQExcercises.cs

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

namespace TestCS
{
	class Program
	{
		static void Main(string[] args) {
			QueryStringArray();
			QueryIntArray();
			QuerryArrayList();
			QuerryCollection();
			QuerryAnimalData();
			Console.ReadKey();
		}

		static void QueryStringArray() {
			string[] dogs = { "K 9", "Brian Griffin", "Scooby Doo", "Old Yeller", "Rin Tin Tin", "Benji", "Charlie B. Barkin", "Lassie", "Snoopy" };
			var dogSpaces = from dog in dogs
							where dog.Contains(" ")
							orderby dog descending
							select dog;
			foreach (var i in dogSpaces) {
				Console.WriteLine(i);
			}
			Console.WriteLine();
		}

		static int[] QueryIntArray() {
			int[] nums = { 5, 10, 15, 20, 25, 30, 35 };
			var gt20 = from num in nums
					   where num > 20
					   orderby num
					   select num;
			foreach (var i in gt20) {
				Console.WriteLine(i);
			}
			Console.WriteLine();
			Console.WriteLine($"Get Type : {gt20.GetType()}");
			var listGT20 = gt20.ToList<int>();
			var arrayGT20 = gt20.ToArray();
			nums[0] = 40;
			foreach (var i in gt20) {
				Console.WriteLine(i);
			}
			Console.WriteLine();
			return arrayGT20;
		}

		static void QuerryArrayList() {
			ArrayList famAnimals = new ArrayList() {
				new Animal {
					Name = "Heidi",
					Height = .8,
					Weight = 18
				},
				new Animal {
					Name = "Shrek",
					Height = 4,
					Weight = 130
				},
				new Animal {
					Name = "Congo",
					Height = 3.8,
					Weight = 90
				}
			};
			var famAnimalEnum = famAnimals.OfType<Animal>();
			var smAnimals = from animal in famAnimalEnum
							where animal.Weight <= 90
							orderby animal.Name
							select animal;
			foreach (var animal in smAnimals) {
				Console.WriteLine(animal);
			}
			Console.WriteLine();
		}

		static void QuerryCollection() {
			var animalList = new List<Animal>() {
				new Animal {
					Name = "German Shepherd",
					Height = 25,
					Weight = 77
				},
				new Animal {
					Name = "Chihuahua",
					Height = 7,
					Weight = 4.4},
				new Animal {
					Name = "Saint Bernard",
					Height = 30,
					Weight = 200
				}
			};
			var bigDogs = from dog in animalList
						  where dog.Weight > 70 && dog.Height > 25
						  orderby dog.Name
						  select dog;
			foreach (var dog in bigDogs) {
				Console.WriteLine(dog);
			}
			Console.WriteLine();
		}

		static void QuerryAnimalData() {
			Animal[] animals = new[] {
				new Animal {
					Name = "German Shepherd",
					Height = 25,
					Weight = 77,
					AnimalID = 1
				},
				new Animal {
					Name = "Chihuahua",
					Height = 7,
					Weight = 4.4,
					AnimalID = 2
				},
				new Animal {
					Name = "Saint Bernard",
					Height = 30,
					Weight = 200,
					AnimalID = 3
				},
				new Animal {
					Name = "Pug",
					Height = 12,
					Weight = 16,
					AnimalID = 1
				},
				new Animal {
					Name = "Beagle",
					Height = 15,
					Weight = 23,
					AnimalID = 2
				}
			};
			Owner[] owners = new[] {
				new Owner {
					Name = "Doug Parks",
					OwnerID = 1
				},
				new Owner {
					Name = "Sally Smith",
					OwnerID = 2
				},
				new Owner {
					Name = "Paul Brooks",
					OwnerID = 3
				}
			};
			var nameHeight = from a in animals
							 select new { a.Name, a.Height };
			Array arrNameHeight = nameHeight.ToArray();
			foreach (var i in arrNameHeight) {
				Console.WriteLine(i.ToString());
			}
			Console.WriteLine();
			var innerJoin = from animal in animals
							join owner in owners
							on animal.AnimalID equals owner.OwnerID
							orderby owner.Name
							select new {
								OwnerName = owner.Name,
								AnimalName = animal.Name
							};
			foreach (var i in innerJoin) {
				Console.WriteLine("{0} owns {1}", i.OwnerName, i.AnimalName);
			}
			Console.WriteLine();
			var groupJoin = from owner in owners
							orderby owner.OwnerID
							join animal in animals
							on owner.OwnerID equals animal.AnimalID
							into ownerGroup
							select new {
								Owner = owner.Name,
								Animals = from owner2 in ownerGroup
										  orderby owner2.Name
										  select owner2
							};
			foreach (var ownerGroup in groupJoin) {
				Console.WriteLine(ownerGroup.Owner);
				foreach (var animal in ownerGroup.Animals) {
					Console.WriteLine("* {0}", animal.Name);
				}
			}
		}
	}
}