C# in Depth

236 CHAPTER 9 Lambda expressions and expression trees9.2.1 Filtering, sorting, and actions on listsIf you remember the FindAll method on List, it takes a Predicate andreturns a new list with all the elements from the original list that match the predicate.The Sort method takes a Comparison and sorts the list accordingly. Finally, theForEach method takes an Action to perform on each element. Listing 9.4 useslambda expressions to provide the delegate instance to each of these methods. Thesample data in question is just the name and year of release for various films. We printout the original list, then create and print out a filtered list of only old films, then sortand print out the original list, ordered by name. (It’s interesting to consider howmuch more code would have been required to do the same thing in C# 1, by the way.)Listing 9.4Manipulating a list of films using lambda expressionsclass Film{public string Name { get; set; }public int Year { get; set; }public override string ToString(){return string.Format("Name={0}, Year={1}", Name, Year);}}...var films = new List{new Film {Name="Jaws", Year=1975},new Film {Name="Singing in the Rain", Year=1952},new Film {Name="Some Like It Hot", Year=1959},new Film {Name="The Wizard of Oz", Year=1939},new Film {Name="It's a Wonderful Life", Year=1946},new Film {Name="American Beauty", Year=1999},new Film {Name="High Fidelity", Year=2000},new Film {Name="The Usual Suspects", Year=1995}};Action print = film => { Console.WriteLine(film); };films.ForEach(print);C Prints original listfilms.FindAll(film => film.Year < 1960).ForEach(print);films.Sort((f1, f2) => f1.Name.CompareTo(f2.Name));films.ForEach(print);Createsreusablelist-printingdelegateThe first half of listing 9.4 involves just setting up the data. I would have used an anonymoustype, but it’s relatively tricky to create a generic list from a collection of anonymoustype instances. (You can do it by creating a generic method that takes an arrayand converts it to a list of the same type, then pass an implicitly typed array into thatmethod. An extension method in .NET 3.5 called ToList provides this functionalitytoo, but that would be cheating as we haven’t looked at extension methods yet!)DCreatesfiltered listEBSortsoriginal listLicensed to Rhona Hadida