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In F#, a map is a special kind of set that associates the values with key. A map is created in a similar way as sets are created.
Creating Maps
Maps are created by creating an empty map using Map.empty and adding items using the Add function. The following example demonstrates this −
Example
(* Create an empty Map *) let students = Map.empty. (* Creating an empty Map *) Add("Zara Ali", "1501"). Add("Rishita Gupta", "1502"). Add("Robin Sahoo", "1503"). Add("Gillian Megan", "1504");; printfn "Map - students: %A" students (* Convert a list to Map *) let capitals = [ "Argentina", "Buenos Aires"; "France ", "Paris"; "Chili", "Santiago"; "Malaysia", " Kuala Lumpur"; "Switzerland", "Bern" ] |> Map.ofList;; printfn "Map capitals : %A" capitals
When you compile and execute the program, it yields the following output −
Map - students: map [("Gillian Megan", "1504"); ("Rishita Gupta", "1502"); ("Robin Sahoo", "1503 "); ("Zara Ali", "1501")] Map capitals : map [("Argentina", "Buenos Aires"); ("Chili", "Santiago"); ("France ", "Paris"); ("Malaysia", " Kuala Lumpur"); ("Switzerland", "Bern")]
You can access individual elements in the map using the key.
Example
(* Create an empty Map *) let students = Map.empty. (* Creating an empty Map *) Add("Zara Ali", "1501"). Add("Rishita Gupta", "1502"). Add("Robin Sahoo", "1503"). Add("Gillian Megan", "1504");; printfn "Map - students: %A" students (*Accessing an element using key *) printfn "%A" students.["Zara Ali"]
When you compile and execute the program, it yields the following output −
Map - students: map [("Gillian Megan", "1504"); ("Rishita Gupta", "1502"); ("Robin Sahoo", "1503 "); ("Zara Ali", "1501")] "1501"
Basic Operations on Maps
Add module name
The following table shows the basic operations on maps −
Member | Description |
---|---|
Add | Returns a new map with the binding added to the given map. |
ContainsKey | Tests if an element is in the domain of the map. |
Count | The number of bindings in the map. |
IsEmpty | Returns true if there are no bindings in the map. |
Item | Lookup an element in the map. Raises KeyNotFoundException if no binding exists in the map. |
Remove | Removes an element from the domain of the map. No exception is raised if the element is not present. |
TryFind | Lookup an element in the map, returning a Some value if the element is in the domain of the map and None if not. |
The following example demonstrates the uses of some of the above functionalities −
Example
(* Create an empty Map *) let students = Map.empty. (* Creating an empty Map *) Add("Zara Ali", "1501"). Add("Rishita Gupta", "1502"). Add("Robin Sahoo", "1503"). Add("Gillian Megan", "1504"). Add("Shraddha Dubey", "1505"). Add("Novonil Sarker", "1506"). Add("Joan Paul", "1507");; printfn "Map - students: %A" students printfn "Map - number of students: %d" students.Count (* finding the registration number of a student*) let found = students.TryFind "Rishita Gupta" match found with | Some x -> printfn "Found %s." x | None -> printfn "Did not find the specified value."
When you compile and execute the program, it yields the following output −
Map - students: map [("Gillian Megan", "1504"); ("Joan Paul", "1507"); ("Novonil Sarker", "1506" ); ("Rishita Gupta", "1502"); ("Robin Sahoo", "1503"); ("Shraddha Dubey", "1505"); ("Zara Ali", "1501")] Map - number of students: 7 Found 1502.
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