C# - Dictionary

The Dictionary<TKey, TValue> is a generic collection that stores key-value pairs in no particular order.

Dictionary Characteristics

  • Dictionary<TKey, TValue> stores key-value pairs.
  • Comes under System.Collections.Generic namespace.
  • Implements IDictionary<TKey, TValue> interface.
  • Keys must be unique and cannot be null.
  • Values can be null or duplicate.
  • Values can be accessed by passing associated key in the indexer e.g. myDictionary[key]
  • Elements are stored as KeyValuePair<TKey, TValue> objects.

Creating a Dictionary

You can create the Dictionary<TKey, TValue> object by passing the type of keys and values it can store. The following example shows how to create a dictionary and add key-value pairs.

Example: Create Dictionary and Add Elements
IDictionary<int, string> numberNames = new Dictionary<int, string>();
numberNames.Add(1,"One"); //adding a key/value using the Add() method
numberNames.Add(2,"Two");
numberNames.Add(3,"Three");

//The following throws run-time exception: key already added.
//numberNames.Add(3, "Three"); 

foreach(KeyValuePair<int, string> kvp in numberNames)
    Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
		
//creating a dictionary using collection-initializer syntax
var cities = new Dictionary<string, string>(){
	{"UK", "London, Manchester, Birmingham"},
	{"USA", "Chicago, New York, Washington"},
	{"India", "Mumbai, New Delhi, Pune"}
};
		
foreach(var kvp in cities)
    Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
Try it

In the above example, numberNames is a Dictionary<int, string> type dictionary, so it can store int keys and string values. In the same way, cities is a Dictionary<string, string> type dictionary, so it can store string keys and string values. Dictionary cannot include duplicate or null keys, whereas values can be duplicated or null. Keys must be unique otherwise, it will throw a runtime exception.

Comments

Post a Comment

Popular posts from this blog

C# | Association, Aggregation and Composition

Image
Association, Aggregation, and Composition are terms that represent relationships among objects. They are very basic stuff of Object-Oriented Programming. Association Association is a relationship among the objects. Association is "*a*" relationship among objects. In Association, the relationship among the objects determines what an object instance can cause another to perform an action on its behalf. We can also say that an association defines the multiplicity among the objects. We can define a one-to-one, one-to-many, many-to-one and many-to-many relationship among objects. Association is a more general term to define a relationship among objects. Association means that an object "uses" another object. For example, Managers and Employees, multiple employees may be associated with a single manager and a single employee may be associated with multiple managers. Aggregation Aggregation is a special type of Association. Aggregation is "*the*" relationship amo...
Read more

Throw vs Throw ex in C#

In C#, the   "throw"   keyword is used to throw an exception when an error occurs in your code. However, there are two variations of the   "throw"   statement:   "throw"   and   "throw ex" . We will look at the distinctions between   "throw"   and   "throw ex"   in C# in this article. In C#, the  "throw"  keyword is used to declare an exception. When an exception is thrown, the code that can handle it uses a catch block to capture it. The  "throw"  keyword is typically used to throw a new exception object, which can be created using the  "new"  keyword. For example, look at the below code: C# Code: try    {        // Some code that could potentially throw an exception    }   catch  (Exception ex)   {        // Handle the exception  ...
Read more

String[] args in C#

String[] args is a parameter of the Main method that represents the command-line arguments passed to the application when it is executed1. For example, if you run your application like this: MyApp.exe arg1 arg2 arg3 The args array will contain three strings: "arg1", "arg2", and "arg3". You can use the args array to access the command-line arguments and perform different actions based on them. For example, you can write a program that copies a file from one location to another by passing the source and destination paths as arguments1. Here is a simple example of how to use String[] args in C#: public   class Program  {       static void Main(string[] args)     {          Console.WriteLine("Number of arguments: " + args.Length);          foreach (string arg in args)         {             Console.WriteLine("Argument: " + arg);       ...
Read more