Lambda and LINQ in C#

1. The fancy stuff Lambda and LINQ in C#

2. Purpose of these slides • Direct the flow of the presentation AND • Serve as a place for you to check details on LINQ stuff • "I remember join was possible but can't remember the details.." These two are equally important

3. Summary • Introduction • Motivation • Lambda expressions • LINQ • References • Q + maybe A

4. 1. Introduction LINQ • Language Integrated Query • Adds native data querying abilities to .NET • Resembles SQL • High level -> performance overhead eg: var CoolPeople = from p in people where p.CoolFactor > 9 select new { name = p.FirstName + ' ' + p.LastName }; Lambda expressions • Mathematically based on lambda calculus • Functional programming • Anonymous functions: defining functions without bounding to indentifier Example: int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int oddNumbers = numbers.Count(n => n % 2 == 1);

5. 2. Motivation • Why learn to use new ways to program when I already know how to do things in a old way?? • Productivity • Readability • In a long run, the results will be better • even though NOW you will be more productive programming in old Java way Lambda: Why is this cool? It allows you to write quick throw away functions without naming them. • 1 row of LINQ can save you from writing 3 nested loops • 1 row of Lambda stuff can save you from writing 2 new methods

6. 3. Lambda / 1 • Anonymous functions • Can be used in fancy ways • ...But in reality (also called: this project) you will most likely use lambda expressions as parameters to LINQ

7. 3. Lambda / 2 • Expression lambdas  (int x, string s) => s.Length > x • Statement lambdas  delegate void TestDelegate(string s);     …     TestDelegate myDel = n => { string s = n + " " + "World";             Console.WriteLine(s); };     myDel("Hello"); • Lambdas with standard query operators  int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };     int oddNumbers = numbers.Count(n => n % 2 == 1);     var firstNumbersLessThan6 = numbers.TakeWhile(n => n < 6);

8. 3. Lambda / 3, example 1 delegate int del(int i); static void Main(string[] args) {     del myDelegate = x => x * x;     int j = myDelegate(5); //j = 25 }

9. 3. Lambda / 4, example 2 Assigning delegate // c# 2.0 employee.SalaryChanged += delegate(Employee sender, double amount)  { Console.Writeline("changed"); } // c# 3.0 employee.SalaryChanged += (sender, amount) => Console.Writeline("changed");

10. 4. LINQ / 1 • Supports ~all the same as SQL • Can be used WITH lambda • Providers • LINQ to objects • LINQ to XML • LINQ to SQL • LINQ to Sharepoint

11. LINQ / 2 supports (according to Wikipedia) • Select • Where • SelectMany • Sum / Min / Max / Average • Aggregate • Join / GroupJoin • Take / TakeWhile • Skip / SkipWhile • OfType • Concat • OrderBy / ThenBy • Reverse • GroupBy • Distinct • Union / Intersect / Except • SequenceEqual • First / FirstOrDefault / Last / LastOrDefault • Single • ElementAt • Any / All / Contains • Count

12. LINQ - Features • Normal syntax • Lambda syntax • Where • Select • Order • Grouping • Set operators •  Aggregate functions •  Joins

13. LINQ example 1 SQL-like syntax  var productInfos =         from p in products         select p;

14. LINQ example 2 Lambda syntax: customers.Where(c => c.City == "London"); You can group expressions. Order: rightmost is most important customers.Where(c => c.Sex == "female").Where(c => c.Age > 20 && c.Age > 16).OrderBy(c => c.FirstName).OrderBy(c => c.LastName);

15. Where public void Linq5() {     string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };     var shortDigits = digits.Where((digit, index) => digit.Length < index);     Console.WriteLine("Short digits:");     foreach (var d in shortDigits)     {         Console.WriteLine("The word {0} is shorter than its value.", d);     } }

16. Select public void Linq10() {     int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };     string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };     var digitOddEvens =         from n in numbers         select new { Digit = strings[n].ToUpper(), Even = (n % 2 == 0) };     foreach (var d in digitOddEvens)     {         Console.WriteLine("The digit {0} is {1}.", d.Digit, d.Even ? "even" : "odd");     } }

17. Order public class CaseInsensitiveComparer : IComparer<string> { public int Compare(string x, string y) { return string.Compare(x, y, StringComparison.OrdinalIgnoreCase); } } class Program { public static void Linq31() { string[] words = { "aPPLE", "AbAcUs", "bRaNcH", "BlUeBeRrY", "ClOvEr", "cHeRry" }; var sortedWords = words.OrderBy(a => a, new CaseInsensitiveComparer()); foreach (var word in sortedWords) { Console.WriteLine(word); } } }

18. Grouping public static void Linq41() { string[] words = { "blueberry", "chimpanzee", "abacus", "banana", "apple", "cheese" }; var wordGroups = from w in words group w by w[0] into g select new { FirstLetter = g.Key, Words = g }; foreach (var g in wordGroups) { Console.WriteLine("Words that start with the letter '{0}':", g.FirstLetter); foreach (var w in g.Words) { Console.WriteLine(w); } } }

19. Set operators Distinct, union, intersect, except public static void Linq46() { int[] factorsOf300 = { 2, 2, 3, 5, 5 }; var uniqueFactors = factorsOf300.Distinct(); Console.WriteLine("Prime factors of 300:"); foreach (var f in uniqueFactors) { Console.WriteLine(f); } }

20. Aggregate functions Count, min, max, sum, average public void Linq79() { string[] words = { "cherry", "apple", "blueberry" }; double totalChars = words.Sum(w => w.Length); Console.WriteLine("There are a total of {0} characters in these words.", totalChars); }

21. Joins          System.Collections.Generic.Dictionary<int, string> names = new Dictionary<int,string>();             names.Add(1, "Panu");             names.Add(2, "Jeesus");             System.Collections.Generic.Dictionary<int, string> addresses = new Dictionary<int,string>();             addresses.Add(1, "Panu");             addresses.Add(2, "Jeesus");             var addressbook =                 from n in names                 join a in addresses on n.Key equals a.Key                 select new { Name = n.Value, Address = a.Value };             foreach (var v in addressbook)             {                 Console.WriteLine(v.Address + ": " + v.Name);             }

22. In the horizon Good reference: http://msdn.microsoft.com/en-us/vcsharp/aa336746.aspx