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C# Lists: Add some elegance to your code
By
Craig Murphy March 31, 2006
A short and to-the-point tutorial that demonstrates how to sort and search using C#'s List object.
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Technologies:
.NET 1.0/1.1,Visual C# .NET |
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Description
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LINQ for Visual C# 2005 is a short yet comprehensive guide to the major features of LINQ. It thoroughly covers LINQ to Objects, LINQ to SQL, LINQ to DataSet, and LINQ to XML.
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It is a fairly common programming scenario to find ourselves with a list of identical objects. In the past, without adequate support from programming languages, we found ourselves writing a lot of searching and sorting code, and that may have put you off using lists in favour of arrays. All that has changed with C# (particularly 2.0) - its implementation of a list makes handling such lists remarkably easy.
For example, given the following class Person:
public class Person
{
public int age;
public string name;
public Person(int age, string name)
{
this.age = age;
this.name = name;
}
}
We can create a list of Person objects and add six people like so:
List<person>people = new List<person>();
people.Add( new Person(50, "Fred"));
people.Add(new Person(30, "John"));
people.Add(new Person(26, "Andrew"));
people.Add(new Person(24, "Xavier"));
people.Add(new Person(5, "Mark"));
people.Add(new Person(6, "Cameron"));
C#'s list mechanism provides us with a number of useful methods. Personally, I find ForEach, FindAll and Sort to be very useful. ForEach allows us access to each item in the list. FindAll allows us to search for objects in the list that match a specific condition. Sort allows us to sort the objects in the list. The following code demonstrates how we might use each of these methods:
Console.WriteLine("Unsorted list");
people.ForEach( delegate(Person p)
{ Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
// Find the young
List<person> young = people.FindAll(delegate(Person p) { return p.age < 25; });
Console.WriteLine("Age is less than 25");
young.ForEach(delegate(Person p)
{ Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
// Sort by name
Console.WriteLine("Sorted list, by name");
people.Sort(delegate(Person p1, Person p2)
{ return p1.name.CompareTo(p2.name); });
people.ForEach( delegate(Person p)
{ Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
// Sort by age
Console.WriteLine("Sorted list, by age");
people.Sort( delegate(Person p1, Person p2)
{ return p1.age.CompareTo(p2.age); });
people.ForEach( delegate(Person p)
{ Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
And here is the output that we should expect:
Unsorted list
50 Fred
30 John
26 Andrew
24 Xavier
5 Mark
6 Cameron
Age is less than 25
24 Xavier
5 Mark
6 Cameron
Sorted list, by name
26 Andrew
6 Cameron
50 Fred
30 John
5 Mark
24 Xavier
Sorted list, by age
5 Mark
6 Cameron
24 Xavier
26 Andrew
30 John
50 Fred
Lists are powerful and result in fewer, and more elegant, lines of code. Hopefully this short example has demonstrated their ease and you will find yourself using them in your day-to-day development activities.
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Craig Murphy
Craig Murphy is employed by a leading professional services consulting firm as a Systems Development Engineer. Craig is also an author, developer, speaker, Microsoft Most Valuable Professional and Certified ScrumMaster. He specialises in: XML, web services, XSLT, TDD, .net and XP. He has extensive experience with Borland Delphi spanning some 10 years. Apart from in-house software, Craig has written applications for major oil companies and local councils. He is currently using C# and Visual Studio 2005.
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