The F# Mutable 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 keys.
Creating of a F# 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 the 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 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"]
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