Learn C#: Lists
Lists in C#
In C#, a list is a generic data structure that can hold any type. Use the new operator and declare the element type in the angle brackets < >.
In the example code, names is a list containing string values. someObjects is a list containing Object instances.
List<string> names = new List<string>();List<Object> someObjects = new List<Object>();
Object Initialization
Values can be provided to a List when it is constructed in a process called object initialization.
Instead of parentheses, use curly braces after the list’s type.
Note that this can ONLY be used at the time of construction.
List<string> cities = new List<string> { "Los Angeles", "New York City", "Dubai" };
Generic Collections
Some collections, like lists and dictionaries, can be associated with various types. Instead of defining a unique class for each possible type, we define them with a generic type T, e.g. List<T>.
These collections are called generic collection types. They are available in the System.Collections.Generic namespace.
The generic type T will often show up in documentation. When using a generic collection in your code, the actual type is specified when the collection is declared or instantiated.
using System.Collections.Generic;List<string> names = new List<string>();List<Object> objs = new List<Object>();Dictionary<string,int> scores = new Dictionary<string, int>();
Limitless Lists
Unlike a C# array, a C# list does not have a limited number of elements. You can add as many items as you like.
// Initialize array with length 2string[] citiesArray = new string[2];citiesArray[0] = "Los Angeles";citiesArray[1] = "New York City";citiesArray[2] = "Dubai"; // Error!// Initialize list; no length neededList<string> citiesList = new List<string>();citiesList.Add("Los Angeles");citiesList.Add("New York City");citiesList.Add("Dubai");
Count Property
The number of elements in a list is stored in the Count property.
In the example code, the Count of citiesList changes as we add and remove values.
List<string> citiesList = new List<string>();citiesList.Add("Los Angeles");Console.WriteLine(citiesList.Count);// Output: 1citiesList.Add("New York City");Console.WriteLine(citiesList.Count);// Output: 2citiesList.Remove("Los Angeles");Console.WriteLine(citiesList.Count);// Output: 1
Remove()
Elements of a list can be removed with the Remove() method. The method returns true if the item is successfully removed; otherwise, false.
In the example code, attempting to remove "Cairo" returns false because that element is not in the citiesList.
List<string> citiesList = new List<string>();citiesList.Add("Los Angeles");citiesList.Add("New York City");citiesList.Add("Dubai");result1 = citiesList.Remove("New York City");// result1 is trueresult2 = citiesList.Remove("Cairo");// result2 is false
Clear()
All elements of a list can be removed with the Clear() method. It returns nothing.
In the example code, the list is initialized with three items. After calling Clear(), there are zero items in the list.
List<string> citiesList = new List<string> { "Delhi", "Los Angeles", "Kiev" };citiesList.Clear();Console.WriteLine(citiesList.Count);// Output: 0
Contains()
In C#, the list method Contains() returns true if its argument exists in the list; otherwise, false.
In the example code, the first call to Contains() returns true because “New York City” is in the list. The second call returns false because “Cairo” is not in the list.
List<string> citiesList = new List<string> { "Los Angeles", "New York City", "Dubai" };result1 = citiesList.Contains("New York City");// result1 is trueresult2 = citiesList.Contains("Cairo");// result2 is false
List Ranges
Unlike elements in a C# array, multiple elements of a C# list can be accessed, added, or removed simultaneously. A group of multiple, sequential elements within a list is called a range.
Some common range-related methods are:
AddRange()InsertRange()RemoveRange()
string[] african = new string[] { "Cairo", "Johannesburg" };string[] asian = new string[] { "Delhi", "Seoul" };List<string> citiesList = new List<string>();// Add two cities to the listcitiesList.AddRange(african);// List: "Cairo", "Johannesburg"// Add two cities to the front of the listcitiesList.InsertRange(0, asian);// List: "Delhi", "Seoul", "Cairo", "Johannesburg"// Remove the second and third cities from the listcitiesList.RemoveRange(1, 2);// List: "Delhi", "Johannesburg"
List Indexing
In C#, elements in a list can be accessed and modified using zero-based indexing, similar to arrays. The indexer syntax, list[index] is used to get or set the value at a specific position in the list.
List<string> citiesList = new List<string>();citiesList.Add("Delhi");// indexing can be used to access and reassign elementsstring city = citiesList[0];citiesList[0] = "New Delhi";
