You may already know the System.Collections.Generic.Dictionary type from C# or VB.NET. The Dictionary<'TKey, 'TValue> class acts as a standard lookup collection, allowing fast retrieval of values based on a unique key.
new keyword.The following example creates a dictionary by calling its constructor as shown below.
let myDictionary = new Dictionary<string, string>()
myDictionary.Add("txt", "notepad.exe");
myDictionary.Add("bmp", "paint.exe");
myDictionary.Add("dib", "paint.exe");
myDictionary.Add("rtf", "wordpad.exe");
printfn "Dictionary: %A" myDictionary
The following are the most commonly used properties in the Dictionary<'TKey, 'TValue> class.
| 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[TKey] | 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>. |
The following are the most commonly used functions in the Dictionary<'TKey, 'TValue> class.
| Function | 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 | Determines whether the specified object is equal to the current object. |
| Finalize | It allows an object to try to free resources and perform other cleanup operations before reclaiming garbage collection. |
| Remove | Removes the value with the specified key from the Dictionary(TKey, TValue). |
| ToString | Returns a string that represents the current object. |
| TryGetValue | Gets the value associated with the specified key. |
The following example uses some of these properties functions.
let capitals = new Dictionary<string, string>()
capitals.Add("Canada", "Ottawa")
capitals.Add("China", "Beijing")
capitals.Add("Russia", "Moscow")
capitals.Add("USA", "Washington D.C.")
printfn"Total %d capitals" capitals.Count
printfn "Capitals: %A" capitals
let capitalOfRussia = capitals.["Russia"]
//printfn ""
printfn "Capital of Russia: %s" capitalOfRussia
//printfn ""
capitals.Remove("China") |> ignore
printfn"Total %d capitals" capitals.Count
printfn "Capitals: %A" capitals