C# Dictionary

A Dictionary<TKey, TValue> is a generic collection that consists of elements as key/value pairs that are not sorted in an order. For example,

Dictionary<int, string> country = new Dictionary<int, string>();

Here, country is a dictionary that contains int type keys and string type values.

Create a Dictionary

To create a dictionary in C#, we need to use the System.Collections.Generic namespace. Here is how we can create a dictionary in C#.

// create a dictionary
Dictionary<dataType1, dataType2> dictionaryName = new Dictionary<dataType1, dataType2>();

Here,

• dictionaryName - name of the dictionary
• dataType1 - datatype of keys
• dataType2 - datatype of values

Example: Create a Dictionary

using System;
using System.Collections;
class Program
{
    public static void Main()
    {
        // create a dictionary 
        Dictionary<int, string> country = new Dictionary<int, string>();

        // add items to dictionary
        country.Add(5, "Brazil");
        country.Add(3, "China");
        country.Add(4, "Usa");

        // print value having key is 3        
        Console.WriteLine("Value having key 3: " + country[3]);
    }
}

Output

Value having key 3: China

In the above example, we have created a dictionary named country.

The keys are of int type and values are of string type.

Basic Operations on Dictionary

In C#, we can perform different operations on a dictionary. We will look at some commonly used Dictionary<TKey, TValue> operations in this tutorial:

• Add Elements
• Access Elements
• Change Elements
• Remove Elements

Let's see how we can perform these operations in detail.

Add Elements in Dictionary

C# provides the Add() method using which we can add elements in the dictionary. For example,

using System;
using System.Collections;
class Program
{
    public static void Main()
    {
        // create a dictionary 
        Dictionary<string, string> mySongs = new Dictionary<string, string>();

        // add items to dictionary
        mySongs.Add("Queen", "Break Free");
        mySongs.Add("Free", "All right now");
        mySongs.Add("Pink Floyd", "The Wall");

    }
}

In the above example, we have created a Dictionary<TKey, TValue> named mySongs.

Here we have added key/value pairs using the Add() method where,

• keys - "Queen", "Free" and "Pink Floyd"
• values - "Break Free", "All right now" and "The Wall"

using System;
using System.Collections;
class Program
{
    public static void Main()
    {
        // create a dictionary and add elements 
        Dictionary<string, string> songs = new Dictionary<string, string>() {
                                                                   { "Queen", "Break Free" },
                                                                   { "Free", "All right now" } }
;
    } 
}

Access Dictionary Elements

We can access the elements inside the dictionary using it's keys. For example,

using System;
using System.Collections;
class Program
{
    public static void Main()
    {
        // create a dictionary 
        Dictionary<string, string> student = new Dictionary<string, string>();

        // add items to dictionary
        student.Add("Name", "Susan");
        student.Add("Faculty", "History");

        // access the value having key "Name"
        Console.WriteLine(student["Name"]);

        // access the value having key "Faculty"
        Console.WriteLine(student["Faculty"]);
    }
}

Output

Susan
History

In the above example, we have accessed the values of the dictionary using their keys:

• student["Name"] - accesses the value whose key is "Name"
• student["Faculty"] - accesses the value whose key is "Faculty"

Iterate through Dictionary

In C#, we can also loop through each element of the dictionary using a foreach loop. For example,

using System;
using System.Collections;
class Program
{
    public static void Main()
    {
        // create a dictionary 
        Dictionary<string, string> car = new Dictionary<string, string>();

        // add items to dictionary
        car.Add("Model", "Hyundai");
        car.Add("Price", "36K");

        // iterate through the car dictionary 
        foreach (KeyValuePair<string, string> items in car)
        {
            Console.WriteLine("{0} : {1}", items.Key, items.Value);
        }
    }
}

Output

Model : Hyundai
Price : 36K

In the above example, we have looped through car using a foreach loop.

Here, the Key and Value property returns a collection containing keys and values in the dictionary.

Change Dictionary Elements

We can change the value of elements in dictionary as:

using System;
using System.Collections;
class Program
{
    public static void Main()
    {
        // create a dictionary 
        Dictionary<string, string> car = new Dictionary<string, string>();

        // add items to dictionary
        car.Add("Model", "Hyundai");
        car.Add("Price", "36K");

        // print the original value
        Console.WriteLine("Value of Model before changing: " + car["Model"]);

        // change the value of "Model" key to "Maruti"
        car["Model"] = "Maruti";

        // print new updated value of "Model"
        Console.WriteLine("Value of Model after changing: " + car["Model"]);
    }
}

Output

Value of Model before changing: Hyundai
Value of Model after changing: Maruti

Here, we have changed the value of the "Model" key in the car dictionary.

Remove Dictionary Elements

To remove the elements inside the dictionary we use:

• Remove() - removes the key/value pair from the dictionary

For example,

using System;
using System.Collections;
class Program
{
    public static void Main()
    {
        // create a dictionary 
        Dictionary<string, string> employee = new Dictionary<string, string>();

        // add items to dictionary
        employee.Add("Name", "Marry");
        employee.Add("Role", "Manager");
        employee.Add("Address", "California");

        Console.WriteLine("Original Dictionary :");

        // iterate through the modified dictionary 
        foreach (KeyValuePair<string, string> items in employee)
        {
            Console.WriteLine("{0} : {1}", items.Key, items.Value);
        }

        // remove value with key "Role"
        employee.Remove("Role");

        Console.WriteLine("\nModified Dictionary :");

        // iterate through the modified dictionary 
        foreach (KeyValuePair<string, string> items in employee)
        {
            Console.WriteLine("{0} : {1}", items.Key, items.Value);
        }
    }
}

Output

Original Dictionary :
Name : Marry
Role : Manager
Address : California

Modified Dictionary :
Name : Marry
Address : California

In the above example, we have removed the element whose key is "Role".

Here, employee.Remove("Role") removes the key/value pair "Role" : "Manager" from the employee dictionary.

So when we iterate through employee we get a modified dictionary.

Note: If you want to remove all the elements of the dictionary, use the Clear() method.

using System;
using System.Collections.Generic;

class Program
{
    public static void Main()
    {
        // create a dictionary named fruits 
        var fruits = new Dictionary<int, string>() {
            {1, "Apple"},
            {2, "Orange"},
        };

        // print value having key 2
        Console.WriteLine(fruits[2]);
    }
}

Orange