// Namespaces required for collections:
using System.Collections
using System.Collections.GenericDon't confuse System.Collections.Generic with the older System.Collections namespace which existed before generics were added to C#.
Microsoft recommends using Generics as they are faster and more type safe.
Some standard C# Collections
Examples will be based on the following Student class, for generating a list of students to work with as a collection of Student objects.
using System;
namespace CollectionsTest
{
public class Student
{
public int Id { get; set; }
public string Firstname { get; set; }
public string Surname { get; set; }
public int Age { get; set; }
/// <summary>
/// Initializes a new instance of the <see cref="T:CollectionsTest.Student"/> class.
/// Simplistic representation of a student
/// </summary>
/// <param name="id">Identifier.</param>
/// <param name="firstname">Firstname.</param>
/// <param name="surname">Surname.</param>
/// <param name="age">Age.</param>
public Student(int id = 0, string firstname = "", string surname = "", int age = 0)
{
Firstname = firstname;
Surname = surname;
Age = age;
Id = id;
}
public override string ToString()
{
return $"{Id} {Firstname} {Surname}, {Age}";
}
}
}Example of working with array lists, showing three different syntax forms.
using System;
using System.Collections;
using System.Collections.Generic;
namespace CollectionsTest
{
/// <summary>
/// Program to demonstrate use of ArrayLists in C#
/// Relies on a Student classes to generate and work on a list of students.
/// </summary>
class MainClass
{
public static void Main()
{
int id = 0;
Student joe = new Student() { Id = id++, Firstname = "Joe", Surname = "Mangwana", Age = 20 };
Student sue = new Student() { Id = id++, Firstname = "Sue", Surname = "Morena", Age = 22 };
Student pat = new Student() { Id = id++, Firstname = "Pat", Surname = "Manhinga", Age = 25 };
Student rat = new Student() { Id = id++, Firstname = "Rat", Surname = "Mopedzi", Age = 30 };
// C# ArrayLists
// ArrayLists are not strongly typed. Just take note of that
ArrayList studentList = new ArrayList();
studentList.Add(joe);, Lists and Dictionary Lists
studentList.Add(sue);
studentList.Add(pat);
studentList.Add(rat);
// Simplified syntax - does same as above
ArrayList studentListSimple = new ArrayList
{
joe,
sue,
pat,
rat
};
// Alternative syntax - creating new students in place
// keynames are required to reference the items, student.Firstname, etc
id = 10;
ArrayList studentArrayList = new ArrayList() {
new Student() { Id = id++, Firstname = "Joe", Surname = "Mangwana", Age = 20 },
new Student() { Id = id++, Firstname = "Sue", Surname = "Morena", Age = 22 },
new Student() { Id = id++, Firstname = "Pat", Surname = "Manhinga", Age = 25 },
new Student() { Id = id++, Firstname = "Rat", Surname = "Mopedzi", Age = 30 }
};
Console.WriteLine("\n --- Printing an ArrayList ---");
foreach (Student student in studentArrayList)
{
Console.WriteLine(student);
}
}
}
}Generic list List``<T>{=html} are strongly typed. They can only be of
one data type
Example showing three syntax forms of working with generic lists.
using System;
using System.Collections;
using System.Collections.Generic;
namespace CollectionsTest
{
/// <summary>
/// Program to demonstrate use of ArrayLists in C#
/// Relies on a Student classes to generate and work on a list of students.
/// </summary>
class MainClass
{
public static void Main()
{
int id = 0;
Student joe = new Student() { Id = id++, Firstname = "Joe", Surname = "Mangwana", Age = 20 };
Student sue = new Student() { Id = id++, Firstname = "Sue", Surname = "Morena", Age = 22 };
Student pat = new Student() { Id = id++, Firstname = "Pat", Surname = "Manhinga", Age = 25 };
Student rat = new Student() { Id = id++, Firstname = "Rat", Surname = "Mopedzi", Age = 30 };
// Generic list. List<T>
// Generic list. long syntax form
List<Student> learnerList = new List<Student>();
learnerList.Add(joe);
learnerList.Add(sue);
learnerList.Add(pat);
learnerList.Add(rat);
// List<T> are strongly typed. Simplified syntax
List<Student> learnerListSimple = new List<Student>
{
joe,
sue,
pat,
rat
};
id = 10;
List<Student> learnerListLong = new List<Student>
{
new Student() { Id = id++, Firstname = "Bri", Surname = "Dudzai", Age = 20 },
new Student() { Id = id++, Firstname = "Day", Surname = "Ringai", Age = 22 },
new Student() { Id = id++, Firstname = "Lot", Surname = "Molena", Age = 25 },
new Student() { Id = id++, Firstname = "Mas", Surname = "Sarudzo", Age = 30 }
};
Console.WriteLine("\n --- Printing from a Generic List ---");
foreach (Student student in learnerListLong)
{
Console.WriteLine(student);
}
// Output
// --- Printing from a Generic List ---
// 10 Bri Dudzai, 20
// 11 Day Ringai, 22
// 12 Lot Molena, 25
// 13 Mas Sarudzo, 30
}
}
}Dictionary Lists are a type of collection that uses key value pairs. Other languages refer to dictionaries as maps or associative arrays.
Keys in a Dictionary List must be unique.
Keyword: Dictionary<Tkey, TValue>
Example showing different syntaxes working with Dictionaries.
using System;
using System.Collections;
using System.Collections.Generic;
namespace CollectionsTest
{
/// <summary>
/// Program to demonstrate use of Dictionary Lists in C#
/// Relies on a Student classes to generate and work on a list of students.
/// </summary>
class MainClass
{
public static void Main()
{
int id = 0;
Student joe = new Student() { Id = id++, Firstname = "Joe", Surname = "Mangwana", Age = 20 };
Student sue = new Student() { Id = id++, Firstname = "Sue", Surname = "Morena", Age = 22 };
Student pat = new Student() { Id = id++, Firstname = "Pat", Surname = "Manhinga", Age = 25 };
Student rat = new Student() { Id = id++, Firstname = "Rat", Surname = "Mopedzi", Age = 30 };
Dictionary<int, Student> studentDictionary = new Dictionary<int, Student>();
studentDictionary.Add(joe.Id, joe);
studentDictionary.Add(sue.Id, sue);
studentDictionary.Add(pat.Id, pat);
studentDictionary.Add(rat.Id, rat);
// Dictionary list - short syntax of the above
Dictionary<int, Student> studentDictionarySimple = new Dictionary<int, Student>
{
{ joe.Id, joe },
{ sue.Id, sue },
{ pat.Id, pat },
{ rat.Id, rat }
};
// Alternative syntax to initialise dictionaries
id = 2;
Dictionary<int, Student> studentDictionaryLong = new Dictionary<int, Student>()
{
[id++] = new Student() { Id = id, Firstname = "Bri", Surname = "Dudzai", Age = 20 },
[id++] = new Student() { Id = id, Firstname = "Day", Surname = "Ringai", Age = 22 },
[id++] = new Student() { Id = id, Firstname = "Lot", Surname = "Molena", Age = 25 },
[id++] = new Student() { Id = id, Firstname = "Mas", Surname = "Sarudzo", Age = 30 }
};
Console.WriteLine("\n --- Print Dictionary List by keys --- ");
foreach (var key in studentDictionaryLong.Keys)
{
Student student = new Student();
student = studentDictionaryLong[key];
Console.WriteLine(student);
}
Console.WriteLine("\n --- Printing Dictionary List using TryGetValue --- ");
foreach (var key in studentDictionaryLong.Keys)
{
Student student = new Student();
if (studentDictionaryLong.TryGetValue(key, out student))
Console.WriteLine(student);
}
Console.WriteLine("\n --- Printing Dictionary List using Key.Value pairs --- ");
foreach (var pair in studentDictionaryLong)
{
// pair.Key, pair.Value to get a key or value
Student student = new Student();
student = pair.Value;
Console.WriteLine(student);
}
Console.WriteLine("\n --- Iterate and print Dictionary values --- ");
foreach (var studentValue in studentDictionaryLong.Values)
{
Student student = new Student();
student = studentValue;
Console.WriteLine(student);
}
// Output
//
// --- Print Dictionary List by keys ---
// 3 Joe Mangwana, 20
// 4 Sue Morena, 22
// 5 Pat Manhinga, 25
// 6 Rat Mopedzi, 30
//
// --- Printing Dictionary List using TryGetValue ---
// 3 Joe Mangwana, 20
// 4 Sue Morena, 22
// 5 Pat Manhinga, 25
// 6 Rat Mopedzi, 30
//
// --- Printing Dictionary List using Key.Value pairs ---
// 3 Joe Mangwana, 20
// 4 Sue Morena, 22
// 5 Pat Manhinga, 25
// 6 Rat Mopedzi, 30
//
// --- Iterate and print Dictionary values ---
// 3 Joe Mangwana, 20
// 4 Sue Morena, 22
// 5 Pat Manhinga, 25
// 6 Rat Mopedzi, 30
//
}
}
}