Sorting a List object using different sort criterias
Posted on August 28, 2007
I have often had a list of objects that i need to sort. This can easyly be done through a SortedList
The List<> type has a method, List<>.Sort(…) that can help out on this. In the example below, I have implemented a Person class, a PersonCollection : List
1 | <br />using System;<br />using System.Collections.Generic;<br />using System.Text;<br />namespace SortingExample<br />{<br /> class Program<br /> {<br /> static void Main(string[] args)<br /> {<br /> // Create a friendscollection<br /> PersonCollection friends = new PersonCollection();<br /> friends.Add(new Person("Kaj", 32));<br /> friends.Add(new Person("Frank", 33));<br /> friends.Add(new Person("Morten", 42));<br /> Console.WriteLine("Age, Asc");<br /> // Sort by age asc<br /> PersonComparer sorter = new PersonComparer(PersonSort.Age, SortDirection.Ascending);<br /> friends.Sort(sorter);<br /> PrintNames(friends);<br /> Console.WriteLine("Age, Desc");<br /> // Sort by age desc<br /> sorter.SortDirection = SortDirection.Descending;<br /> friends.Sort(sorter);<br /> PrintNames(friends);<br /> Console.WriteLine("Name, Asc");<br /> // Sort by name asc<br /> sorter.SortDirection = SortDirection.Ascending;<br /> sorter.Sort = PersonSort.Name;<br /> friends.Sort(sorter);<br /> PrintNames(friends);<br /> Console.WriteLine("Name, Desc");<br /> // Sort by name desc<br /> sorter.SortDirection = SortDirection.Descending;<br /> friends.Sort(sorter);<br /> PrintNames(friends);<br /> }<br /> |
1 | /// <summary><br /> /// Printing out the persons of a PersonCollection<br /> /// </summary><br /> /// <param name="persons">A list of persons.</param><br /> public static void PrintNames(PersonCollection persons)<br /> {<br /> foreach (Person friend in persons)<br /> {<br /> Console.WriteLine(string.Format("{0} - {1} years", friend.Name, friend.Age));<br /> }<br /> }<br /> } |
1 | <br /> /// <summary><br /> /// The personobject will hold info about a person.<br /> /// </summary><br /> public class Person<br /> {<br /> private string _name;<br /> private int _age;<br /> <br /> /// <summary><br /> /// The name of the person.<br /> /// </summary><br /> public string Name<br /> {<br /> get { return _name; }<br /> set { _name = value; }<br /> }<br /><br /> /// <summary><br /> /// The age of the person.<br /> /// </summary><br /> public int Age<br /> {<br /> get { return _age; }<br /> set { _age = value; }<br /> }<br /><br /> /// <summary><br /> /// Initialize the person object with a name and an age.<br /> /// </summary><br /> /// <param name="name">The name of the person.</param><br /> /// <param name="age">The age of the person.</param><br /> public Person(string name, int age)<br /> {<br /> Name = name;<br /> Age = age;<br /> }<br /> }<br /><br /> /// <summary><br /> /// A list of persons...<br /> /// </summary><br /> public class PersonCollection : List<person><br /> {<br /> }<br /><br /> /// <summary><br /> /// The different sort orders<br /> /// </summary><br /> public enum PersonSort<br /> {<br /> Name,<br /> Age<br /> }<br /><br /> /// <summary><br /> /// Sort direction<br /> /// </summary><br /> /// <remarks>The emum values are used for multiplying on a compare result.<br /> /// This makes descending sorts appear in reverse order.<br /> /// </remarks><br /> public enum SortDirection<br /> {<br /> Ascending = 1,<br /> Descending = -1<br /> }<br /><br /> /// <summary><br /> /// This class takes care of comparing two persons. The<br /> /// class uses sorting and sort direction to determine which<br /> /// of the two objects has the highest value.<br /> /// </summary><br /> public class PersonComparer : IComparer<person><br /> {<br /> private PersonSort _sort;<br /> private SortDirection _sortDirection;<br /> public PersonSort Sort<br /> {<br /> get { return this._sort; }<br /> set { this._sort = value; }<br /> }<br /> public SortDirection SortDirection<br /> {<br /> get { return this._sortDirection; }<br /> set { this._sortDirection = value; }<br /> }<br /><br /> public PersonComparer(PersonSort sort, SortDirection direction)<br /> {<br /> this._sort = sort;<br /> this._sortDirection = direction;<br /> }<br /> #region IComparer<person> Members<br /> public int Compare(Person x, Person y)<br /> {<br /> if (_sort == PersonSort.Age)<br /> {<br /> return x.Age.CompareTo(y.Age)*(int)_sortDirection;<br /> }<br /> else<br /> {<br /> return x.Name.CompareTo(y.Name)*(int)_sortDirection;<br /> }<br /> }<br /> #endregion<br /> }<br />}<br /> |