Some Linq Tips

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace BlogCode
{
    public class Person
    {
        public int Id { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public int Age { get; set; }

        public IEnumerable<Address> Addresses { get; set; }
    }

    public class Address
    {
        public int Id { get; set; }

        public int HouseNumber { get; set; }

        public string Street { get; set; }

        public string City { get; set; }

        public string State { get; set; }

        public string ZipCode { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            IEnumerable<Person> people = new List<Person>();

            var numberOfSteves = people.Count(p => p.FirstName == "Steve");

            var hasZPeople = people.Any(p => p.LastName.StartsWith("Z"));

            var canEveryoneDrink = people.All(p => p.Age > 21);

            var allAddresses = people.SelectMany(p => p.Addresses);

            var person3 = people.SingleOrDefault(p => p.Id == 3);

            var firstName = people.Select(p => p.FirstName);
            var lastName = people.Select(p => p.LastName);

            firstName.Zip(lastName, (first, last) => new Person
            {
                FirstName = first,
                LastName = last
            });

            people.SelectMany(p => p.Addresses.Select(a => new
            {
                p.FirstName,
                p.LastName,
                a.HouseNumber,
                a.Street,
                a.City,
                a.State,
                a.ZipCode
            }));

            people = new List<Person>
                {
                    new Person
                    {
                        Id = 1,
                        FirstName = "Jen"
                    },
                    new Person
                    {
                        Id = 2,
                        FirstName = "Will"
                    },
                    new Person
                    {
                        Id = 3,
                        FirstName = "Jen"
                    }
                };

            var aa = people.First(); // id: 1, FirstName: Jen
            var bb = people.FirstOrDefault(); // id: 1, FirstName: Jen
            var cc = people.Single(); // Exception!
            var dd = people.SingleOrDefault(); // Exception!

            var ee = people.First(p => p.FirstName == "Jen"); // id: 1, FirstName: Jen
            var ff = people.FirstOrDefault(p => p.FirstName == "Jen"); // id: 1, FirstName: Jen
            var gg = people.Single(p => p.FirstName == "Jen"); // Exception!
            var hh = people.SingleOrDefault(p => p.FirstName == "Jen"); // Exception!

            var ii = people.First(p => p.FirstName == "Will"); // id: 2, FirstName: Will
            var jj = people.FirstOrDefault(p => p.FirstName == "Will"); // id: 2, FirstName: Will
            var kk = people.Single(p => p.FirstName == "Will"); // id: 2, FirstName: Will
            var ll = people.SingleOrDefault(p => p.FirstName == "Will"); // id: 2, FirstName: Will

            var mm = people.First(p => p.FirstName == "Steve"); // Exception!
            var nn = people.FirstOrDefault(p => p.FirstName == "Steve"); // null
            var oo = people.Single(p => p.FirstName == "Steve"); // Exception!
            var pp = people.SingleOrDefault(p => p.FirstName == "Steve"); // null
        }
    }
}