C# Dictionary class is a generic collection of keys and values pair of data. The Dictionary class defined in the System.Collections.Generic namespace is a generic class and can store any data types in a form of keys and values. Each key must be unique in the collection.
Before you use the Dictionary class in your code, you must import the System.Collections.Generic namespace using the following line.
- using System.Collections.Generic;
1. Add elements to a C# Dictionary
C# Dictionary class constructor takes a key data type and a value data type. Both types are generic so it can be any .NET data type.
The following Dictionary class is a generic class and can store any data types. This class is defined in the code snippet creates a dictionary where both keys and values are string types.
- Dictionary<string, string> EmployeeList = new Dictionary<string, string>();
The following code snippet adds items to the dictionary.
- EmployeeList.Add("Mahesh Chand", "Programmer");
- EmployeeList.Add("Praveen Kumar", "Project Manager");
- EmployeeList.Add("Raj Kumar", "Architect");
- EmployeeList.Add("Nipun Tomar", "Asst. Project Manager");
- EmployeeList.Add("Dinesh Beniwal", "Manager");
The following code snippet creates a dictionary where the key type is string and value type is short integer.
- Dictionary<string, Int16> AuthorList = new Dictionary<string, Int16>();
The following code snippet adds items to the dictionary.
- AuthorList.Add("Mahesh Chand", 35);
- AuthorList.Add("Mike Gold", 25);
- AuthorList.Add("Praveen Kumar", 29);
- AuthorList.Add("Raj Beniwal", 21);
- AuthorList.Add("Dinesh Beniwal", 84);
We can also limit the size of a dictionary. The following code snippet creates a dictionary where the key type is string and value type is float and total number of items it can hold is 3.
- Dictionary<string, float> PriceList = new Dictionary<string, float>(3);
The following code snippet adds items to the dictionary.
- PriceList.Add("Tea", 3.25f);
- PriceList.Add("Juice", 2.76f);
- PriceList.Add("Milk", 1.15f);
2. Retrieve elements from a C# Dictionary
The Dictionary is a collection. We can use the foreach loop to go through all the items and read them using they Key ad Value properties.
- foreach (KeyValuePair<string, Int16> author in AuthorList)
- {
- Console.WriteLine("Key: {0}, Value: {1}", author.Key, author.Value);
- }
The following code snippet creates a new dictionary and reads all of its items and displays on the console.
- public void CreateDictionary()
- {
-
- Dictionary<string, Int16> AuthorList = new Dictionary<string, Int16>();
- AuthorList.Add("Mahesh Chand", 35);
- AuthorList.Add("Mike Gold", 25);
- AuthorList.Add("Praveen Kumar", 29);
- AuthorList.Add("Raj Beniwal", 21);
- AuthorList.Add("Dinesh Beniwal", 84);
-
- Console.WriteLine("Authors List");
- foreach (KeyValuePair<string, Int16> author in AuthorList)
- {
- Console.WriteLine("Key: {0}, Value: {1}", author.Key, author.Value);
- }
- }
-
3. C# Dictionary Properties
The Dictionary class has three properties – Count, Keys and Values.
4. Get number of elements in a C# dictionary
The Count property gets the number of key/value pairs in a Dictionary.
The following code snippet display number of items in a dictionary.
- Console.WriteLine("Count: {0}", AuthorList.Count);
5. Get a Dictionary item
The Item property gets and sets the value associated with the specified key.
The following code snippet sets and gets an items value.
-
- AuthorList["Mahesh Chand"] = 20;
-
- Int16 age = Convert.ToInt16(AuthorList["Mahesh Chand"]);
6. Get the collection of keys of C# Dictionary
The Keys property gets a collection containing the keys in the Dictionary. It returns an object of KeyCollection type.
The following code snippet reads all keys in a Dictionary.
-
- Dictionary<string, Int16>.KeyCollection keys = AuthorList.Keys;
- foreach (string key in keys)
- {
- Console.WriteLine("Key: {0}", key);
- }
7. Get the collection of values of a C# Dictionary
The Values property gets a collection containing the values in the Dictionary. It returns an object of ValueCollection type.
The following code snippet reads all values in a Dictionary.
-
- Dictionary<string, Int16>.ValueCollection values = AuthorList.Values;
- foreach (Int16 val in values)
- {
- Console.WriteLine("Value: {0}", val);
- }
8. C# Dictionary Methods
The Dictionary class is a generic collection and provides all common methods to add, remove, find and replace items in the collection.
9. Add Items
The Add method adds an item to the Dictionary collection in form of a key and a value.
The following code snippet creates a Dictionary and adds an item to it by using the Add method.
- Dictionary<string, Int16> AuthorList = new Dictionary<string, Int16>();
- AuthorList.Add("Mahesh Chand", 35);
Alternatively, we can use the Item property. If the key does not exist in the collection, a new item is added. If the same key already exists in the collection, the item value is updated to the new value.
The following code snippet adds an item and updates the existing item in the collection.
- AuthorList["Neel Beniwal"] = 9;
- AuthorList["Mahesh Chand"] = 20;
10. Remove elements from a C# dictionary
The Remove method removes an item with the specified key from the collection. The following code snippet removes an item.
-
- AuthorList.Remove("Mahesh Chand");
The Clear method removes all items from the collection. The following code snippet removes all items by calling the Clear method.
11. Find a Key in a Dictionary
The ContainsKey method checks if a key is already exists in the dictionary. The following code snippet checks if a key is already exits and if not, add one.
- if (!AuthorList.ContainsKey("Mahesh Chand"))
- {
- AuthorList["Mahesh Chand"] = 20;
- }
12. Find a Value in a Dictionary
The ContainsValue method checks if a value is already exists in the dictionary. The following code snippet checks if a value is already exits.
- if (!AuthorList.ContainsValue(9))
- {
- Console.WriteLine("Item found");
- }
13. C# Dictionary Code Example
Here is the complete sample code showing how to use these methods.
-
- Dictionary<string, Int16> AuthorList = new Dictionary<string, Int16>();
- AuthorList.Add("Mahesh Chand", 35);
- AuthorList.Add("Mike Gold", 25);
- AuthorList.Add("Praveen Kumar", 29);
- AuthorList.Add("Raj Beniwal", 21);
- AuthorList.Add("Dinesh Beniwal", 84);
-
- Console.WriteLine("Count: {0}", AuthorList.Count);
-
- AuthorList["Neel Beniwal"] = 9;
- if (!AuthorList.ContainsKey("Mahesh Chand"))
- {
- AuthorList["Mahesh Chand"] = 20;
- }
- if (!AuthorList.ContainsValue(9))
- {
- Console.WriteLine("Item found");
- }
-
-
- Console.WriteLine("Authors all items:");
- foreach (KeyValuePair<string, Int16> author in AuthorList)
- {
- Console.WriteLine("Key: {0}, Value: {1}",
- author.Key, author.Value);
- }
-
- AuthorList.Remove("Mahesh Chand");
-
- AuthorList.Clear();
14. Summary
In this tutorial, we learned about the basic use of a dictionary using C# language. We also saw how to create a dictionary using the Dictionary class in C# and .NET. After that, we learned how to use various methods and properties of the class.