F# - Mutable Dictionary

The Dictionary<'TKey, 'TValue> class is the mutable analog of the F# map data structure and contains many of the same functions.
Recapitulating from the Map chapter in F#, a map is a special kind of set that associates the values with key.

Creating of a Mutable Dictionary

Mutable dictionaries are created using the new keyword and calling the list's constructor. The following example demonstrates this −

open System.Collections.Generic
let dict = new Dictionary<string, string>()
dict.Add("1501", "Zara Ali")
dict.Add("1502","Rishita Gupta")
dict.Add("1503","Robin Sahoo")
dict.Add("1504","Gillian Megan")
printfn "Dictionary - students: %A" dict

When you compile and execute the program, it yields the following output −

Dictionary - students: seq
[[1501, Zara Ali]; [1502, Rishita Gupta]; [1503, Robin Sahoo];
[1504, Gillian Megan]]

The Dictionary(TKey,TValue) Class

The Dictionary(TKey, TValue) Class represents a collection of keys and values.
The following tables provide the properties, constructors and the methods of the List(T) class −

Properties

Property	Description
Comparer	Gets the IEqualityComparer(T) that is used to determine equality of keys for the dictionary.
Count	Gets the number of key/value pairs contained in the Dictionary(TKey, TValue).
Item	Gets or sets the value associated with the specified key.
Keys	Gets a collection containing the keys in the Dictionary(TKey, TValue).
Values	Gets a collection containing the values in the Dictionary(TKey, TValue).

Constructors

Constructors	Description
Dictionary(TKey, TValue)()	Initializes a new instance of the Dictionary(TKey, TValue) class that is empty, has the default initial capacity, and uses the default equality comparer for the key type.
Dictionary(TKey, TValue)(IDictionary(TKey, TValue))	Initializes a new instance of the Dictionary(TKey, TValue) class that contains elements copied from the specified IDictionary(TKey, TValue) and uses the default equality comparer for the key type.
Dictionary(TKey, TValue)(IEqualityComparer(TKey))	Initializes a new instance of the Dictionary(TKey, TValue) class that is empty, has the default initial capacity, and uses the specified IEqualityComparer(T).
Dictionary(TKey, TValue)(Int32)	Initializes a new instance of the Dictionary(TKey, TValue) class that is empty, has the specified initial capacity, and uses the default equality comparer for the key type.
Dictionary(TKey, TValue)(IDictionary(TKey, TValue), IEqualityComparer(TKey))	Initializes a new instance of the Dictionary(TKey, TValue) class that contains elements copied from the specified IDictionary(TKey, TValue) and uses the specified IEqualityComparer(T).
Dictionary(TKey, TValue)(Int32, IEqualityComparer(TKey))	Initializes a new instance of the Dictionary(TKey, TValue) class that is empty, has the specified initial capacity, and uses the specified IEqualityComparer(T).
Dictionary(TKey, TValue)(SerializationInfo, StreamingContext)	Initializes a new instance of the ictionary(TKey, TValue) class with serialized data.

Methods

Method	Description
Add	Adds the specified key and value to the dictionary.
Clear	Removes all keys and values from the Dictionary(TKey, TValue).
ContainsKey	Determines whether the Dictionary(TKey, TValue) contains the specified key.
ContainsValue	Determines whether the Dictionary(TKey, TValue) contains a specific value.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object.)
Finalize	Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
GetEnumerator	Returns an enumerator that iterates through the Dictionary(TKey, TValue).
GetHashCode	Serves as the default hash function. (Inherited from Object.)
GetObjectData	Implements the System.Runtime.Serialization.ISerializable interface and returns the data needed to serialize the Dictionary(TKey, TValue)instance.
GetType	Gets the Type of the current instance. (Inherited from Object.)
MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
OnDeserialization	Implements the System.Runtime.Serialization.ISerializable interface and raises the deserialization event when the deserialization is complete.
Remove	Removes the value with the specified key from the Dictionary(TKey, TValue).
ToString	Returns a string that represents the current object. (Inherited from Object.)
TryGetValue	Gets the value associated with the specified key.

Example

open System.Collections.Generic
let dict = new Dictionary<string, string>()

dict.Add("1501", "Zara Ali")
dict.Add("1502","Rishita Gupta")
dict.Add("1503","Robin Sahoo")
dict.Add("1504","Gillian Megan")

printfn "Dictionary - students: %A" dict
printfn "Total Number of Students: %d" dict.Count
printfn "The keys: %A" dict.Keys
printf"The Values: %A" dict.Values

When you compile and execute the program, it yields the following output −

Dictionary - students: seq
[[1501, Zara Ali]; [1502, Rishita Gupta]; [1503, Robin Sahoo];
[1504, Gillian Megan]]
Total Number of Students: 4
The keys: seq ["1501"; "1502"; "1503"; "1504"]
The Values: seq ["Zara Ali"; "Rishita Gupta"; "Robin Sahoo"; "Gillian Megan"]