Dictionary

C# Dictionary

• The Dictionary<TKey, TValue> class is a generic collection class in the System.Collection.Generics namespace. TKey denotes the type of key and TValue is the type of TValue.
• There is a non-generic collection called a Hashtable, which does the same thing, except that it operates on type object. However, you want to avoid the non-generic collections and use their generic counterparts instead
• Dictionary cannot include duplicate or null keys, where as values can be duplicated or set as null. Keys must be unique otherwise it will throw a runtime exception.
• The capacity of a Dictionary is the number of elements that Dictionary can hold.

Properties

Property	Description
Count	Gets the total number of elements exists in the Dictionary<TKey,TValue>              .
IsReadOnly	Returns a boolean indicating whether the Dictionary<TKey,TValue> is read-only.
Item	Gets or sets the element with the specified key in the Dictionary<TKey,TValue>.
Keys	Returns collection of keys of Dictionary<TKey,TValue>.
Values	Returns collection of values in Dictionary<TKey,TValue>.

Methods

Method	Description
Add	Add key-value pairs in Dictionary<TKey, TValue> collection.
Remove	Removes the first occurrence of specified item from the Dictionary<TKey, TValue>.
ContainsKey	Checks whether the specified key exists in Dictionary<TKey, TValue>.
ContainsValue	Checks whether the specified key exists in Dictionary<TKey, TValue>.
Clear	Removes all the elements from Dictionary<TKey, TValue>.
TryGetValue	Returns true and assigns the value with specified key, if key does not exists then return false.

Example

 public static void Main(String[] args)

   {

           

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

            // Adding key/value pairs  

            _dictionary.Add(1, "Hello");

            _dictionary.Add(2, "This is");

            _dictionary.Add(3, "Blog for C#");

            _dictionary.Remove(1); //Remove value which key is 1

            Console.WriteLine("Is Key Exist?: {0}",_dictionary.ContainsKey(2));//Return True

            Console.WriteLine("Is Value Exist?: {0}", _dictionary.ContainsValue("This is"));//Return True

            foreach (KeyValuePair<int, string> ele1 in _dictionary)

            {

                Console.WriteLine("{0} and {1}",

                          ele1.Key, ele1.Value);

            }

            Console.ReadLine();

           

    }