using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass { public static void Main() { string[] presidents = {"G", "H", "a", "H", "over", "Jack"}; string name = presidents.Take(0).FirstOrDefault(); Console.WriteLine(name == null ? "NULL" : name); } }
FirstOrDefault returns null when an Element Is Found
using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass { public static void Main() { string[] presidents = {"G", "H", "a", "H", "over", "Jack"}; string name = presidents.FirstOrDefault(); Console.WriteLine(name == null ? "NULL" : name); } }
FirstOrDefault with string operator
using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass { public static void Main() { string[] presidents = {"G", "H", "a", "H", "over", "Jack"}; string name = presidents.FirstOrDefault(p => p.StartsWith("B")); Console.WriteLine(name == null ? "NULL" : name); } }
FirstOrDefault with Condition
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
public static void Main() {
List
Product product789 = products.FirstOrDefault(p => p.Id == 789);
Console.WriteLine(“Product 789 exists: {0}”, product789 != null);
}
static List
List
empTree.Add(new Product { ProductName = “A”, Category = “O”, UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “B”, Category = “O”, UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 2 });
empTree.Add(new Product { ProductName = “C”, Category = “O”, UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 3 });
empTree.Add(new Product { ProductName = “D”, Category = “O”, UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 4 });
empTree.Add(new Product { ProductName = “E”, Category = “O”, UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 5 });
empTree.Add(new Product { ProductName = “F”, Category = “O”, UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 6 });
return empTree;
}
}
class Product : IComparable
public string ProductName { get; set; }
public string Category { get; set; }
public int UnitPrice { get; set; }
public int UnitsInStock { get; set; }
public int Total { get; set; }
public DateTime OrderDate { get; set; }
public int Id { get; set; }
public override string ToString() {
return String.Format(“Id: {0}, Name: {1} , Category: {3}”, this.Id, this.ProductName, this.Category);
}
int IComparable
if (other == null)
return 1;
if (this.Id > other.Id)
return 1;
if (this.Id < other.Id) return -1; return 0; } } [/csharp]
use FirstOrDefault
using System; using System.Collections; using System.Collections.Generic; using System.Text; using System.Linq; public class MainClass{ public static void Main(){ int[] numbers = { 1, 3, 5, 7, 9 }; var query = numbers.FirstOrDefault(n => n % 2 == 0); Console.WriteLine("The first even element in the sequence"); Console.Write(query); Console.WriteLine("The last odd element in the sequence"); query = numbers.LastOrDefault(n => n % 2 == 1); Console.Write(query); } }
First operator
using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass { public static void Main() { string[] presidents = {"G", "H", "a", "H", "over", "Jack"}; string name = presidents.First(); Console.WriteLine(name); } }
First with string method
using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass { public static void Main() { string[] presidents = {"G", "H", "a", "H", "over", "Jack"}; string name = presidents.First(p => p.StartsWith("H")); Console.WriteLine(name); } }