Dictionaries are a data structure where a key/value pairs are stored. There are some rules for dictionaries:

  • Keys in dictionaries must be unique. You cannot have duplicate keys. You can have duplicate values.

  • Keys cannot be null. Values can be null.

  • Only elements of the same type can be stored in a dictionary.

  • A dictionary’s capacity depends on how many elements a dictionary has the capability of holding.

Structure of a dictionary

The structure of a dictionary is as follows:

Dictionary<Tkey, TValue>

Creating a dictionary

In order to create a dictionary, we first need to import the appropriate namespace:

using System.Collections.Generic;

Let’s say we want to create a dictionary that has keys of type int and values of type string. This is how we do it:

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

var users = new Dictionary<int,string>();

Inserting data into a dictionary

In order to insert data into a dictionary, we use the Add method:

users.Add(1, "Sys Admin");
users.Add(2, "Network Admin");
users.Add(3, "grahamb");
users.Add(4, "petersonj");

Checking for a key in a dictionary

If we want to find if a particular key is in a dictionary, we use the ContainsKey method:

Console.WriteLine(users.ContainsKey(4)); //True

Checking for a value in a dictionary

If on the other hand, we want to find a value, we use the ContainsValue method:

Console.WriteLine(users.ContainsValue("petersonj")); //True

Removing data from a dictionary

In order to remove data from a dictionary, we use the Remove method along with the key:

Console.WriteLine(users.Remove(1)); //True

Clearing a dictionary

If we want to clear the entire dictionary, we use the Clear method: